Materiały źródłowe

• #1

  https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)

  There are around a billion cases of seasonal influenza annually, including 35 million cases of severe illness. […] It causes 290 000 to 650 000 respiratory deaths annually. […] Ninety-nine percent of deaths in children under 5 years of age with influenza-related lower respiratory tract infections are in developing countries. […] Influenza A and B viruses circulate and cause seasonal epidemics of disease. […] Hospitalization and death due to influenza occur mainly among high-risk groups. […] The effects of seasonal influenza epidemics in developing countries are not fully known, but research estimates that 99% of deaths in children under 5 years of age with influenza related lower respiratory tract infections are in developing countries. […] People at greater risk of severe disease or complications when infected are pregnant women, children under 5 years of age, older people, individuals with chronic medical conditions and individuals with immunosuppressive conditions/treatments.

• #2 Influenza: Practice Essentials, Background, Pathophysiology

  https://emedicine.medscape.com/article/219557-overview

  Influenza, one of the most common infectious diseases, is a highly contagious airborne disease that occurs in seasonal epidemics and manifests as an acute febrile illness with variable degrees of systemic symptoms, ranging from mild fatigue to respiratory failure and death. Influenza causes significant loss of workdays, human suffering, and mortality. […] The WHO estimates that 1 billion influenza cases, 3 to 5 million severe cases, and 290,000 to 650,000 influenza-related respiratory deaths occur each year worldwide. […] In the United States, individual cases of seasonal flu and flu-related deaths in adults are not reportable illnesses; consequently, mortality is estimated by using statistical models. […] The CDC estimates that flu-associated deaths in the United States ranged from about 3000 to 49,000 annually between 1976 and 2006.

• #3 Influenza: Practice Essentials, Background, Pathophysiology

  https://emedicine.medscape.com/article/219557-overview

  Unlike adult flu-related deaths, pediatric flu-related deaths are reportable in the United States. […] For the 2019-2020 influenza season, the CDC reports an estimated 35 million influenza-associated illnesses, 16 million influenza-related medical visits, 380,000 flu-associated hospitalizations, and 20,000 influenza-related deaths. […] The 1918 H1N1 influenza pandemic caused 500,000-700,000 deaths in the United Statesalmost 200,000 of them in October 1918 aloneand an estimated 30-40 million deaths worldwide, mostly among people aged 15-35 years. […] The 2009-2010 influenza season was affected by the H1N1 (swine flu) influenza epidemic, the first wave of which hit the United States in the spring of 2009, followed by a second, larger wave in the fall and winter; activity peaked in October and then quickly declined to below baseline levels by January 2010.

• #4 Influenza (Flu) – Epidemiology

  https://www.vdh.virginia.gov/epidemiology/epidemiology-fact-sheets/influenza/

  Seasonal influenza is commonly referred to as the flu. It is a contagious respiratory illness caused by influenza viruses. Flu can cause mild to severe illness, and at times can lead to death. Flu viruses can be detected year-round in the United States, but they are most common during the fall and winter. […] There are two types of flu viruses that cause human seasonal illness: Types A and B. Type A has many different subtypes based on proteins on the surface of the virus that tend to change from year to year. Type B viruses generally change more slowly compared to type A influenza viruses. […] Anyone can get flu and develop serious illness. However, some people are at higher risk of developing serious flu-related complications if they get sick. This includes young children (under the age of five years, but especially those younger than two years, pregnant women, people aged 65 years and older, and people with chronic illnesses (e.g., lung disease, heart disease, cancer, or diabetes) or weakened immune systems.

• #5

  https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)

  There are around a billion cases of seasonal influenza annually, including 35 million cases of severe illness. […] It causes 290 000 to 650 000 respiratory deaths annually. […] Ninety-nine percent of deaths in children under 5 years of age with influenza-related lower respiratory tract infections are in developing countries. […] Influenza A and B viruses circulate and cause seasonal epidemics of disease. […] Hospitalization and death due to influenza occur mainly among high-risk groups. […] The effects of seasonal influenza epidemics in developing countries are not fully known, but research estimates that 99% of deaths in children under 5 years of age with influenza related lower respiratory tract infections are in developing countries. […] People at greater risk of severe disease or complications when infected are pregnant women, children under 5 years of age, older people, individuals with chronic medical conditions and individuals with immunosuppressive conditions/treatments.

• #6

  https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)

  There are around a billion cases of seasonal influenza annually, including 35 million cases of severe illness. […] It causes 290 000 to 650 000 respiratory deaths annually. […] Ninety-nine percent of deaths in children under 5 years of age with influenza-related lower respiratory tract infections are in developing countries. […] Influenza A and B viruses circulate and cause seasonal epidemics of disease. […] Hospitalization and death due to influenza occur mainly among high-risk groups. […] The effects of seasonal influenza epidemics in developing countries are not fully known, but research estimates that 99% of deaths in children under 5 years of age with influenza related lower respiratory tract infections are in developing countries. […] People at greater risk of severe disease or complications when infected are pregnant women, children under 5 years of age, older people, individuals with chronic medical conditions and individuals with immunosuppressive conditions/treatments.

• #7 WHO EMRO | Influenza surveillance | Influenza | Health topics

  https://www.emro.who.int/health-topics/influenza/influenza-surveillance.html

  Influenza surveillance is the collection, compilation and analysis of information on influenza activity in a defined population. This could be a country, specific population groups or a region. Data are collected over a defined period of time and reported for the purposes of monitoring influenza activity to facilitate the undertaking early actions to stop or minimize its transmission. The purpose of systematic surveillance of influenza activity is to: […] better understand when and where influenza activity is occurring; […] determine which influenza viruses are circulating; […] detect changes (mutations) in influenza virus; and […] measure the impact influenza is having on illness, hospitalizations and deaths. […] Influenza surveillance is conducted through passive, active and sentinel surveillance methods. Passive surveillance is the routine collection of data from fixed sites, such as outpatient wards and hospitals. Active surveillance is the collection of reported cases that are reported to health authorities. These reports can come from hospitals and the community. Sentinel surveillance is a network of purpose-built reporting sites, where more detailed information and samples are collected from people that fit the surveillance criteria. Sentinel surveillance can supplement existing passive systems with more detailed information, without overburdening existing national disease surveillance systems.

• #8 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  It is important to maintain a comprehensive system for influenza surveillance for the following reasons: Influenza viruses are constantly undergoing minor changes (this is commonly referred to as „antigenic drift”), and ongoing data collection and characterization of viruses helps to monitor these changes. […] Surveillance of viruses can detect these changes and help inform the public health response. […] Annual vaccination is recommended, and vaccines are updated regularly based on surveillance findings. […] Treatment recommendations for influenza virus infection are informed by laboratory surveillance for antiviral resistance. […] Influenza surveillance and targeted research studies are used to monitor the impact of influenza on different segments of the population (e.g., people in certain age groups, people with underlying medical conditions) and the impact of influenza prevention measures such as vaccines.

• #9 WHO EMRO | Influenza surveillance | Influenza | Health topics

  https://www.emro.who.int/health-topics/influenza/influenza-surveillance.html

  Influenza viruses are constantly changing, therefore ongoing data collection and characterization of viruses is required. […] Surveillance of viruses will detect these changes and inform the public health response, such as virus-specific vaccine development. […] Vaccines must be administered annually and are updated regularly based on surveillance findings. […] Influenza surveillance and targeted research studies are used to monitor the impact of influenza on different groups in a population (e.g. certain age groups, people with underlying health conditions, etc.). […] Influenza surveillance data help estimate influenza burden of disease study (of severe diseases, hospitalization and deaths), which in turn contribute to vaccine effectiveness studies and the development of new vaccines.

• #10 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  It is important to maintain a comprehensive system for influenza surveillance for the following reasons: Influenza viruses are constantly undergoing minor changes (this is commonly referred to as „antigenic drift”), and ongoing data collection and characterization of viruses helps to monitor these changes. […] Surveillance of viruses can detect these changes and help inform the public health response. […] Annual vaccination is recommended, and vaccines are updated regularly based on surveillance findings. […] Treatment recommendations for influenza virus infection are informed by laboratory surveillance for antiviral resistance. […] Influenza surveillance and targeted research studies are used to monitor the impact of influenza on different segments of the population (e.g., people in certain age groups, people with underlying medical conditions) and the impact of influenza prevention measures such as vaccines.

• #11 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  It is important to maintain a comprehensive system for influenza surveillance for the following reasons: Influenza viruses are constantly undergoing minor changes (this is commonly referred to as „antigenic drift”), and ongoing data collection and characterization of viruses helps to monitor these changes. […] Surveillance of viruses can detect these changes and help inform the public health response. […] Annual vaccination is recommended, and vaccines are updated regularly based on surveillance findings. […] Treatment recommendations for influenza virus infection are informed by laboratory surveillance for antiviral resistance. […] Influenza surveillance and targeted research studies are used to monitor the impact of influenza on different segments of the population (e.g., people in certain age groups, people with underlying medical conditions) and the impact of influenza prevention measures such as vaccines.

• #12 WHO EMRO | Influenza surveillance | Influenza | Health topics

  https://www.emro.who.int/health-topics/influenza/influenza-surveillance.html

  Influenza viruses are constantly changing, therefore ongoing data collection and characterization of viruses is required. […] Surveillance of viruses will detect these changes and inform the public health response, such as virus-specific vaccine development. […] Vaccines must be administered annually and are updated regularly based on surveillance findings. […] Influenza surveillance and targeted research studies are used to monitor the impact of influenza on different groups in a population (e.g. certain age groups, people with underlying health conditions, etc.). […] Influenza surveillance data help estimate influenza burden of disease study (of severe diseases, hospitalization and deaths), which in turn contribute to vaccine effectiveness studies and the development of new vaccines.

• #13 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  It is important to maintain a comprehensive system for influenza surveillance for the following reasons: Influenza viruses are constantly undergoing minor changes (this is commonly referred to as „antigenic drift”), and ongoing data collection and characterization of viruses helps to monitor these changes. […] Surveillance of viruses can detect these changes and help inform the public health response. […] Annual vaccination is recommended, and vaccines are updated regularly based on surveillance findings. […] Treatment recommendations for influenza virus infection are informed by laboratory surveillance for antiviral resistance. […] Influenza surveillance and targeted research studies are used to monitor the impact of influenza on different segments of the population (e.g., people in certain age groups, people with underlying medical conditions) and the impact of influenza prevention measures such as vaccines.

• #14 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  It is important to maintain a comprehensive system for influenza surveillance for the following reasons: Influenza viruses are constantly undergoing minor changes (this is commonly referred to as „antigenic drift”), and ongoing data collection and characterization of viruses helps to monitor these changes. […] Surveillance of viruses can detect these changes and help inform the public health response. […] Annual vaccination is recommended, and vaccines are updated regularly based on surveillance findings. […] Treatment recommendations for influenza virus infection are informed by laboratory surveillance for antiviral resistance. […] Influenza surveillance and targeted research studies are used to monitor the impact of influenza on different segments of the population (e.g., people in certain age groups, people with underlying medical conditions) and the impact of influenza prevention measures such as vaccines.

• #15 WHO EMRO | Influenza surveillance | Influenza | Health topics

  https://www.emro.who.int/health-topics/influenza/influenza-surveillance.html

  Influenza viruses are constantly changing, therefore ongoing data collection and characterization of viruses is required. […] Surveillance of viruses will detect these changes and inform the public health response, such as virus-specific vaccine development. […] Vaccines must be administered annually and are updated regularly based on surveillance findings. […] Influenza surveillance and targeted research studies are used to monitor the impact of influenza on different groups in a population (e.g. certain age groups, people with underlying health conditions, etc.). […] Influenza surveillance data help estimate influenza burden of disease study (of severe diseases, hospitalization and deaths), which in turn contribute to vaccine effectiveness studies and the development of new vaccines.

• #16 WHO EMRO | Influenza surveillance | Influenza | Health topics

  https://www.emro.who.int/health-topics/influenza/influenza-surveillance.html

  The WHOs Global Influenza Programme (GIP) provides global standards for influenza surveillance. In addition, GIP collects and analyses virological and epidemiological influenza surveillance data from around the world. […] The regular sharing of quality influenza surveillance and monitoring data by countries allows WHO to: […] describe critical features of influenza epidemiology, including risk groups, transmission characteristics, and impact; […] monitor global trends in influenza transmission; and […] support the selection of influenza strains for vaccine production. […] Due to the constant evolving nature of influenza viruses, the WHO Global Influenza Surveillance and Response System (GISRS) a system of national influenza centres and WHO collaborating centres around the world continuously monitors the influenza viruses circulating in humans and updates the composition of influenza vaccines twice a year. […] The mission of GISRS is to protect people from the threat of influenza by continuously functioning as a: […] global mechanism of surveillance, preparedness and response for seasonal, pandemic and zoonotic influenza; […] global platform for monitoring influenza epidemiology and disease; and […] global alert for novel influenza viruses and other respiratory pathogens.

• #17 WHO EMRO | Influenza surveillance | Influenza | Health topics

  https://www.emro.who.int/health-topics/influenza/influenza-surveillance.html

  The WHOs Global Influenza Programme (GIP) provides global standards for influenza surveillance. In addition, GIP collects and analyses virological and epidemiological influenza surveillance data from around the world. […] The regular sharing of quality influenza surveillance and monitoring data by countries allows WHO to: […] describe critical features of influenza epidemiology, including risk groups, transmission characteristics, and impact; […] monitor global trends in influenza transmission; and […] support the selection of influenza strains for vaccine production. […] Due to the constant evolving nature of influenza viruses, the WHO Global Influenza Surveillance and Response System (GISRS) a system of national influenza centres and WHO collaborating centres around the world continuously monitors the influenza viruses circulating in humans and updates the composition of influenza vaccines twice a year. […] The mission of GISRS is to protect people from the threat of influenza by continuously functioning as a: […] global mechanism of surveillance, preparedness and response for seasonal, pandemic and zoonotic influenza; […] global platform for monitoring influenza epidemiology and disease; and […] global alert for novel influenza viruses and other respiratory pathogens.

• #18 WHO EMRO | Influenza surveillance | Influenza | Health topics

  https://www.emro.who.int/health-topics/influenza/influenza-surveillance.html

  The WHOs Global Influenza Programme (GIP) provides global standards for influenza surveillance. In addition, GIP collects and analyses virological and epidemiological influenza surveillance data from around the world. […] The regular sharing of quality influenza surveillance and monitoring data by countries allows WHO to: […] describe critical features of influenza epidemiology, including risk groups, transmission characteristics, and impact; […] monitor global trends in influenza transmission; and […] support the selection of influenza strains for vaccine production. […] Due to the constant evolving nature of influenza viruses, the WHO Global Influenza Surveillance and Response System (GISRS) a system of national influenza centres and WHO collaborating centres around the world continuously monitors the influenza viruses circulating in humans and updates the composition of influenza vaccines twice a year. […] The mission of GISRS is to protect people from the threat of influenza by continuously functioning as a: […] global mechanism of surveillance, preparedness and response for seasonal, pandemic and zoonotic influenza; […] global platform for monitoring influenza epidemiology and disease; and […] global alert for novel influenza viruses and other respiratory pathogens.

• #19 Overview of Influenza Surveillance in the United States | Seasonal Influenza (Flu) | CDC

  http://medbox.iiab.me/modules/en-cdc/espanol.cdc.gov/enes/flu/weekly/overview.htm

  The Epidemiology and Prevention Branch in the Influenza Division at CDC collects, compiles and analyzes information on influenza activity year-round in the United States and produces FluView, a weekly influenza surveillance report, and FluView Interactive, which allows for more in-depth exploration of influenza surveillance data. […] The U.S. influenza surveillance system is a collaborative effort between CDC and its many partners in state, local, and territorial health departments, public health and clinical laboratories, vital statistics offices, healthcare providers, clinics, and emergency departments. […] Information in five categories is collected from eight different data sources that allows CDC to: Find out when and where influenza activity is occurring, Track influenza-related illness, Determine what influenza viruses are circulating, Detect changes in influenza viruses, Measure the impact influenza is having on hospitalizations and deaths.

• #20 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  The Influenza Division at CDC collects, compiles, and analyzes information on influenza activity year-round in the United States. Included below is a summary of the components of the U.S. Influenza Surveillance System to which data are reported weekly and presented in FluView, CDC’s influenza surveillance report. […] FluView, a weekly influenza surveillance report, and FluView Interactive, an online application that allows for more in-depth exploration of influenza surveillance data, are updated each week. The data presented each week are preliminary and may change as more data are received. […] The U.S. influenza surveillance system is a collaborative effort between CDC and its many partners in state, local, and territorial health departments, public health and clinical laboratories, vital statistics offices, health care providers, hospitals, clinics, emergency departments, and long-term care facilities. Information in five categories is collected from nine data sources in order to: Find out when and where influenza activity is occurring; Determine what influenza viruses are circulating; Detect changes in influenza viruses; and Measure the impact influenza is having on illness, hospitalizations, and deaths.

• #21 European Influenza Surveillance Network (EISN)

  https://www.ecdc.europa.eu/en/about-us/partnerships-and-networks/disease-and-laboratory-networks/eisn

  The European Influenza Surveillance Network (EISN) is coordinated by ECDC. The network combines epidemiological and virological surveillance of influenza to provide decision makers and public health experts in EU/EEA Member States with the information required to better assess influenza activity in Europe and take appropriate action. Ultimately, EISN aims to contribute to reducing the burden of disease associated with influenza in Europe. […] Virological surveillance activities are coordinated through the European Reference Laboratory Network for Human Influenza (ERLI-Net), a sub-network within EISN. […] The following epidemiological and virological influenza surveillance data are collected through The European Surveillance System (TESSy) database hosted by ECDC: […] On an operational level, EISN consists of operational contact points for influenza epidemiology and virology.

• #22 Surveillance for seasonal influenza

  https://www.ecdc.europa.eu/en/seasonal-influenza/surveillance-reports-and-disease-data

  ECDC collects epidemiological and virological data from the EU/EEA Member States. The surveillance data reported comes largely from sentinel influenza surveillance systems, which cover a subset of the population in each country. […] Several countries also conduct surveillance of hospitalised cases. A sample of cases is also tested to determine virus characteristics. […] The weekly surveillance of seasonal influenza is complemented by epidemic intelligence activities at ECDC, which encompass monitoring of official and unofficial sources on outbreaks and other influenza-related developments. […] ECDCs influenza virus characterisation reports are published periodically and give an overview of circulating influenza viruses. They provide details on the current vaccine strains, summarise the development of the viruses since the last report, and closely follow the main developments for the ongoing influenza season.

• #23 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  Approximately 100 public health and approximately 300 clinical laboratories located throughout all 50 states, Puerto Rico, Guam, and the District of Columbia participate in virologic surveillance for influenza through either the U.S. Influenza Collaborating Laboratories System or NREVSS. […] All public health and clinical laboratories report each week to CDC the total number of respiratory specimens tested for influenza and the number positive for influenza viruses, along with age or age group of the person, if available. […] In order to use each data source most appropriately and to avoid duplication, reports from public health and clinical laboratories are presented separately in both FluView and FluView Interactive. […] The age distribution of people who have tested positive for influenza reported from public health laboratories can be visualized in FluView Interactive.

• #24 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  This includes genetic and antigenic characterization. […] The goals of genetic and antigenic characterization are to assess how similar the currently circulating influenza viruses are to viruses used to produce current influenza vaccines and to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. […] CDC also analyzes influenza viruses collected by public health laboratories for susceptibility to influenza antivirals, including neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and a PA cap-dependent endonuclease inhibitor (baloxavir). […] In 2007, human infection with a novel influenza A virus became a nationally notifiable condition in the United States. […] Rapid detection and reporting of human infections with novel influenza A viruses viruses against which there is often little to no pre-existing immunity in the population is important to facilitate prompt awareness and characterization of influenza A viruses with pandemic potential and accelerate the implementation of public health responses to limit the transmission and impact of these viruses.

• #25 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  Information on outpatient visits to health care providers for respiratory illness referred to as influenza-like illness [ILI) is collected through the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet). […] The national percentage of patient visits to healthcare providers for ILI reported each week is calculated by combining state-specific data weighted by state population. […] The reporting period for each influenza season begins during Morbidity and Mortality Weekly Report (MMWR) week 40 and ends week 39 of the following year. […] The timing of the annual „Flu season” as determined by elevated flu activity also varies from season to season.

• #26 Weekly US Influenza Surveillance Report: Key Updates for Week 17, ending April 26, 2025 | FluView | CDC

  https://www.cdc.gov/fluview/surveillance/2025-week-17.html

  CDC estimates that there have been at least 47 million illnesses, 610,000 hospitalizations, and 26,000 deaths from flu so far this season. […] CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as influenza viruses are circulating. […] There are prescription flu antiviral drugs that can treat flu illness; those should be started as early as possible and are especially important for patients at higher risk for severe illness. […] Influenza viruses are among several viruses contributing to respiratory disease activity. CDC is providing updated, integrated information about COVID-19, flu, and respiratory syncytial virus (RSV) activity on a weekly basis. […] The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population.

• #27 Weekly US Influenza Surveillance Report: Key Updates for Week 17, ending April 26, 2025 | FluView | CDC

  https://www.cdc.gov/fluview/surveillance/2025-week-17.html

  A total of 39,053 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2024, and April 26, 2025. […] The cumulative hospitalization rate observed in Week 17 was 127.4 per 100,000 population, which is the highest cumulative hospitalization rate for all seasons since 2010-2011. […] Twelve influenza-associated pediatric deaths occurring during the 2024-2025 season were reported to CDC during Week 17. […] A total of 216 influenza-associated pediatric deaths occurring during the 2024-2025 season have been reported to CDC. This number of pediatric deaths exceeds the previous high reported for a regular (non-pandemic) flu season.

• #28 Influenza: Canadian respiratory virus surveillance report (FluWatch+) — Canada.ca

  https://health-infobase.canada.ca/respiratory-virus-surveillance/influenza.html

  Weekly overview of key trends in influenza (flu) activity in Canada. […] The epidemic threshold is 5% tests positive for influenza. When it is exceeded, and a minimum of 15 weekly influenza detections are reported, a seasonal influenza epidemic is declared. […] Outbreaks of laboratory-confirmed influenza in high-risk settings (long-term care facilities, acute care facilities, retirement facilities, remote and/or isolated communities and other settings) are reported from provincial and territorial public health departments. […] Hospitalizations, ICU admissions, and deaths associated with influenza (influenza type/subtype), by age or age group, are reported from provincial and territorial public health departments. […] Vaccine monitoring refers to activities related to the monitoring of influenza vaccine coverage and vaccine effectiveness.

• #29 WHO EMRO | Influenza surveillance | Influenza | Health topics

  https://www.emro.who.int/health-topics/influenza/influenza-surveillance.html

  Influenza surveillance is the collection, compilation and analysis of information on influenza activity in a defined population. This could be a country, specific population groups or a region. Data are collected over a defined period of time and reported for the purposes of monitoring influenza activity to facilitate the undertaking early actions to stop or minimize its transmission. The purpose of systematic surveillance of influenza activity is to: […] better understand when and where influenza activity is occurring; […] determine which influenza viruses are circulating; […] detect changes (mutations) in influenza virus; and […] measure the impact influenza is having on illness, hospitalizations and deaths. […] Influenza surveillance is conducted through passive, active and sentinel surveillance methods. Passive surveillance is the routine collection of data from fixed sites, such as outpatient wards and hospitals. Active surveillance is the collection of reported cases that are reported to health authorities. These reports can come from hospitals and the community. Sentinel surveillance is a network of purpose-built reporting sites, where more detailed information and samples are collected from people that fit the surveillance criteria. Sentinel surveillance can supplement existing passive systems with more detailed information, without overburdening existing national disease surveillance systems.

• #30 WHO EMRO | Influenza surveillance | Influenza | Health topics

  https://www.emro.who.int/health-topics/influenza/influenza-surveillance.html

  Influenza surveillance is the collection, compilation and analysis of information on influenza activity in a defined population. This could be a country, specific population groups or a region. Data are collected over a defined period of time and reported for the purposes of monitoring influenza activity to facilitate the undertaking early actions to stop or minimize its transmission. The purpose of systematic surveillance of influenza activity is to: […] better understand when and where influenza activity is occurring; […] determine which influenza viruses are circulating; […] detect changes (mutations) in influenza virus; and […] measure the impact influenza is having on illness, hospitalizations and deaths. […] Influenza surveillance is conducted through passive, active and sentinel surveillance methods. Passive surveillance is the routine collection of data from fixed sites, such as outpatient wards and hospitals. Active surveillance is the collection of reported cases that are reported to health authorities. These reports can come from hospitals and the community. Sentinel surveillance is a network of purpose-built reporting sites, where more detailed information and samples are collected from people that fit the surveillance criteria. Sentinel surveillance can supplement existing passive systems with more detailed information, without overburdening existing national disease surveillance systems.

• #31 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  Approximately 100 public health and approximately 300 clinical laboratories located throughout all 50 states, Puerto Rico, Guam, and the District of Columbia participate in virologic surveillance for influenza through either the U.S. Influenza Collaborating Laboratories System or NREVSS. […] All public health and clinical laboratories report each week to CDC the total number of respiratory specimens tested for influenza and the number positive for influenza viruses, along with age or age group of the person, if available. […] In order to use each data source most appropriately and to avoid duplication, reports from public health and clinical laboratories are presented separately in both FluView and FluView Interactive. […] The age distribution of people who have tested positive for influenza reported from public health laboratories can be visualized in FluView Interactive.

• #32 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  Information on outpatient visits to health care providers for respiratory illness referred to as influenza-like illness [ILI) is collected through the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet). […] The national percentage of patient visits to healthcare providers for ILI reported each week is calculated by combining state-specific data weighted by state population. […] The reporting period for each influenza season begins during Morbidity and Mortality Weekly Report (MMWR) week 40 and ends week 39 of the following year. […] The timing of the annual „Flu season” as determined by elevated flu activity also varies from season to season.

• #33 Weekly US Influenza Surveillance Report: Key Updates for Week 17, ending April 26, 2025 | FluView | CDC

  https://www.cdc.gov/fluview/surveillance/2025-week-17.html

  CDC estimates that there have been at least 47 million illnesses, 610,000 hospitalizations, and 26,000 deaths from flu so far this season. […] CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as influenza viruses are circulating. […] There are prescription flu antiviral drugs that can treat flu illness; those should be started as early as possible and are especially important for patients at higher risk for severe illness. […] Influenza viruses are among several viruses contributing to respiratory disease activity. CDC is providing updated, integrated information about COVID-19, flu, and respiratory syncytial virus (RSV) activity on a weekly basis. […] The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population.

• #34 Weekly US Influenza Surveillance Report: Key Updates for Week 17, ending April 26, 2025 | FluView | CDC

  https://www.cdc.gov/fluview/surveillance/2025-week-17.html

  A total of 39,053 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2024, and April 26, 2025. […] The cumulative hospitalization rate observed in Week 17 was 127.4 per 100,000 population, which is the highest cumulative hospitalization rate for all seasons since 2010-2011. […] Twelve influenza-associated pediatric deaths occurring during the 2024-2025 season were reported to CDC during Week 17. […] A total of 216 influenza-associated pediatric deaths occurring during the 2024-2025 season have been reported to CDC. This number of pediatric deaths exceeds the previous high reported for a regular (non-pandemic) flu season.

• #35 Influenza: Canadian respiratory virus surveillance report (FluWatch+) — Canada.ca

  https://health-infobase.canada.ca/respiratory-virus-surveillance/influenza.html

  Weekly overview of key trends in influenza (flu) activity in Canada. […] The epidemic threshold is 5% tests positive for influenza. When it is exceeded, and a minimum of 15 weekly influenza detections are reported, a seasonal influenza epidemic is declared. […] Outbreaks of laboratory-confirmed influenza in high-risk settings (long-term care facilities, acute care facilities, retirement facilities, remote and/or isolated communities and other settings) are reported from provincial and territorial public health departments. […] Hospitalizations, ICU admissions, and deaths associated with influenza (influenza type/subtype), by age or age group, are reported from provincial and territorial public health departments. […] Vaccine monitoring refers to activities related to the monitoring of influenza vaccine coverage and vaccine effectiveness.

• #36 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  The Influenza Division at CDC collects, compiles, and analyzes information on influenza activity year-round in the United States. Included below is a summary of the components of the U.S. Influenza Surveillance System to which data are reported weekly and presented in FluView, CDC’s influenza surveillance report. […] FluView, a weekly influenza surveillance report, and FluView Interactive, an online application that allows for more in-depth exploration of influenza surveillance data, are updated each week. The data presented each week are preliminary and may change as more data are received. […] The U.S. influenza surveillance system is a collaborative effort between CDC and its many partners in state, local, and territorial health departments, public health and clinical laboratories, vital statistics offices, health care providers, hospitals, clinics, emergency departments, and long-term care facilities. Information in five categories is collected from nine data sources in order to: Find out when and where influenza activity is occurring; Determine what influenza viruses are circulating; Detect changes in influenza viruses; and Measure the impact influenza is having on illness, hospitalizations, and deaths.

• #37 WHO EMRO | Influenza surveillance | Influenza | Health topics

  https://www.emro.who.int/health-topics/influenza/influenza-surveillance.html

  The WHOs Global Influenza Programme (GIP) provides global standards for influenza surveillance. In addition, GIP collects and analyses virological and epidemiological influenza surveillance data from around the world. […] The regular sharing of quality influenza surveillance and monitoring data by countries allows WHO to: […] describe critical features of influenza epidemiology, including risk groups, transmission characteristics, and impact; […] monitor global trends in influenza transmission; and […] support the selection of influenza strains for vaccine production. […] Due to the constant evolving nature of influenza viruses, the WHO Global Influenza Surveillance and Response System (GISRS) a system of national influenza centres and WHO collaborating centres around the world continuously monitors the influenza viruses circulating in humans and updates the composition of influenza vaccines twice a year. […] The mission of GISRS is to protect people from the threat of influenza by continuously functioning as a: […] global mechanism of surveillance, preparedness and response for seasonal, pandemic and zoonotic influenza; […] global platform for monitoring influenza epidemiology and disease; and […] global alert for novel influenza viruses and other respiratory pathogens.

• #38 Surveillance for seasonal influenza

  https://www.ecdc.europa.eu/en/seasonal-influenza/surveillance-reports-and-disease-data

  ECDC collects epidemiological and virological data from the EU/EEA Member States. The surveillance data reported comes largely from sentinel influenza surveillance systems, which cover a subset of the population in each country. […] Several countries also conduct surveillance of hospitalised cases. A sample of cases is also tested to determine virus characteristics. […] The weekly surveillance of seasonal influenza is complemented by epidemic intelligence activities at ECDC, which encompass monitoring of official and unofficial sources on outbreaks and other influenza-related developments. […] ECDCs influenza virus characterisation reports are published periodically and give an overview of circulating influenza viruses. They provide details on the current vaccine strains, summarise the development of the viruses since the last report, and closely follow the main developments for the ongoing influenza season.

• #39 Influenza Activity, Surveillance and Reports – New York State Department of Health

  https://www.health.ny.gov/diseases/communicable/influenza/surveillance/

  The New York State Department of Health (NYSDOH) collects, compiles, and analyzes information on flu activity year-round in New York State (NYS), and produces a weekly report during the flu season (October through the following May). […] In view of persisting elevated influenza activity throughout NYS, NYSDOH is extending the surveillance season beyond May until influenza activity has decreased.

• #40 Influenza – Wikipedia

  https://en.wikipedia.org/wiki/Influenza

  Influenza is typically characterized by seasonal epidemics and sporadic pandemics. […] Most of the burden of influenza is a result of flu seasons caused by influenza A virus and influenza B virus. […] In a typical year, influenza viruses infect 5-15% of the global population, causing 35 million cases of severe illness annually and accounting for 290,000-650,000 deaths each year due to respiratory illness. […] The reported number of influenza cases is usually much lower than the actual number. […] During seasonal epidemics, it is estimated that about 80% of otherwise healthy people who have a cough or sore throat have the flu. […] Approximately 30-40% of people hospitalized for influenza develop pneumonia, and about 5% of all severe pneumonia cases in hospitals are due to influenza, which is also the most common cause of ARDS in adults.

• #41 Influenza (Flu) – Epidemiology

  https://www.vdh.virginia.gov/epidemiology/epidemiology-fact-sheets/influenza/

  Seasonal influenza is commonly referred to as the flu. It is a contagious respiratory illness caused by influenza viruses. Flu can cause mild to severe illness, and at times can lead to death. Flu viruses can be detected year-round in the United States, but they are most common during the fall and winter. […] There are two types of flu viruses that cause human seasonal illness: Types A and B. Type A has many different subtypes based on proteins on the surface of the virus that tend to change from year to year. Type B viruses generally change more slowly compared to type A influenza viruses. […] Anyone can get flu and develop serious illness. However, some people are at higher risk of developing serious flu-related complications if they get sick. This includes young children (under the age of five years, but especially those younger than two years, pregnant women, people aged 65 years and older, and people with chronic illnesses (e.g., lung disease, heart disease, cancer, or diabetes) or weakened immune systems.

• #42 Influenza Surveillance Reports – Health Protection Surveillance Centre

  https://www.hpsc.ie/a-z/respiratory/influenza/seasonalinfluenza/surveillance/influenzasurveillancereports/

  In the Northern Hemisphere, influenza season commences in October and continues through to May. In general influenza outbreaks last between 6 – 8 weeks and can affect all ages, in particular the extremes of age. Influenza surveillance can provide information that may help in the management of such an outbreak. […] Influenza surveillance involves collection of both clinical and virological data. Clinical surveillance monitors the impact of the illness on the health service and the community, while virological surveillance confirms that influenza is circulating and also identifies the current strain. […] As there is little difference in the presenting symptoms of a number of respiratory pathogens, virological confirmation is required to identify that influenza is the causative agent. The NVRL can detect and identify if influenza A and/or B viruses are circulating. Further identification of subtypes of influenza A isolates is also carried out. Samples received at the NVRL undergo polymerase chain reaction studies, cell culture and virus isolation. […] Following collection of the data, an Integrated Respiratory Virus Bulletin is compiled.

• #43 Human Influenza Epidemiology

  https://pmc.ncbi.nlm.nih.gov/articles/PMC8634793/

  Influenza virus infections are common in people of all ages. Epidemics occur in the winter months in temperate locations and at varying times of the year in subtropical and tropical locations. […] Vaccination is the most effective measure to prevent infections, and in recent years influenza vaccines have become the most frequently used vaccines in the world. Nonpharmaceutical public health measures can also be effective in reducing transmission, allowing suppression or mitigation of influenza epidemics and pandemics. […] Measures of influenza incidence include the number or rate of infections that have occurred, are occurring, or are predicted to occur in a population. […] In most influenza epidemics, the incidence of infections is higher in children than adults. […] The immune response to an influenza virus infection can include production of antibodies specific to that strain, and serologic surveillance of the prevalence of antibody in a population over time can provide direct information on the cumulative incidence of infections.

• #44 Influenza: epidemiology and hospital management

  https://pmc.ncbi.nlm.nih.gov/articles/PMC8624711/

  Innovative technologies, new pharmaceuticals and improved global surveillance are changing the way healthcare systems respond to influenza and other diseases to ensure global health resilience and effective management of future outbreaks. […] Seasonal influenza is a common cause of respiratory infection during the winter months in Northern and Southern Hemispheres, and can occur all year round in tropical and subtropical areas. […] Annual seasonal influenza epidemics result in around 290,000650,000 deaths worldwide and infect up to 20% of the population, depending on circulating viral strains. […] At the time of writing, there are reduced levels of influenza globally compared with previous years, probably secondary to the non-pharmacological interventions (social distancing, hand hygiene) implemented to reduce severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission.

• #45 Influenza (Flu) | Disease Outbreak Control Division

  https://health.hawaii.gov/docd/disease_listing/influenza-flu/

  Influenza, commonly called the flu, is caused by the influenza virus, which infects the respiratory tract (nose, throat, lungs). […] Influenza viruses are spread person-to-person via large respiratory droplets through coughing and sneezing. […] The exact timing and duration of each flu season varies from year to year, but influenza activity usually begins to increase during October. […] Vaccination is recommended each year due to the constant evolving nature of influenza viruses. […] For more information on influenza surveillance in Hawaii, see our weekly, seasonal, and archived reports below. […] Negative results of RIDTs do not exclude influenza infection in patients with signs and symptoms suggestive of influenza and should be interpreted with caution given that false negatives are common, especially when influenza activity is high. […] There are three FDA-approved influenza antiviral drugs recommended by CDC for this flu season: oseltamivir (Tamiflu), zanamivir (Relenza), and peramivir (Rapivab).

• #46 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  Information on outpatient visits to health care providers for respiratory illness referred to as influenza-like illness [ILI) is collected through the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet). […] The national percentage of patient visits to healthcare providers for ILI reported each week is calculated by combining state-specific data weighted by state population. […] The reporting period for each influenza season begins during Morbidity and Mortality Weekly Report (MMWR) week 40 and ends week 39 of the following year. […] The timing of the annual „Flu season” as determined by elevated flu activity also varies from season to season.

• #47 Human Influenza Epidemiology

  https://pmc.ncbi.nlm.nih.gov/articles/PMC8634793/

  Influenza virus infections are common in people of all ages. Epidemics occur in the winter months in temperate locations and at varying times of the year in subtropical and tropical locations. […] Vaccination is the most effective measure to prevent infections, and in recent years influenza vaccines have become the most frequently used vaccines in the world. Nonpharmaceutical public health measures can also be effective in reducing transmission, allowing suppression or mitigation of influenza epidemics and pandemics. […] Measures of influenza incidence include the number or rate of infections that have occurred, are occurring, or are predicted to occur in a population. […] In most influenza epidemics, the incidence of infections is higher in children than adults. […] The immune response to an influenza virus infection can include production of antibodies specific to that strain, and serologic surveillance of the prevalence of antibody in a population over time can provide direct information on the cumulative incidence of infections.

• #48 Azthena logo with the word Azthena

  https://www.news-medical.net/health/Influenza-Epidemiology.aspx

  Influenza is a highly infectious viral disease that can occur as a pandemic, epidemic, outbreak and in form of sporadic cases. A majority of human infections are caused by either type A or B influenza viruses. Type A has been associated with widespread epidemics and pandemics, while type B has been infrequently implicated in regional epidemics. Influenza type C infections cause only a mild respiratory illness. […] Yearly influenza epidemics can affect all populations, but children younger than the age of two, adults older than 65, as well as people with chronic medical conditions or weakened immune systems, bear the highest risk of complications. The annual attack rate is estimated at 510% in adults and 2030% in children. […] The epidemics caused by the influenza virus are estimated to result in about 3 to 5 million cases of severe illness, and up to 500 thousand deaths worldwide.

• #49

  https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)

  There are around a billion cases of seasonal influenza annually, including 35 million cases of severe illness. […] It causes 290 000 to 650 000 respiratory deaths annually. […] Ninety-nine percent of deaths in children under 5 years of age with influenza-related lower respiratory tract infections are in developing countries. […] Influenza A and B viruses circulate and cause seasonal epidemics of disease. […] Hospitalization and death due to influenza occur mainly among high-risk groups. […] The effects of seasonal influenza epidemics in developing countries are not fully known, but research estimates that 99% of deaths in children under 5 years of age with influenza related lower respiratory tract infections are in developing countries. […] People at greater risk of severe disease or complications when infected are pregnant women, children under 5 years of age, older people, individuals with chronic medical conditions and individuals with immunosuppressive conditions/treatments.

• #50

  https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)

  There are around a billion cases of seasonal influenza annually, including 35 million cases of severe illness. […] It causes 290 000 to 650 000 respiratory deaths annually. […] Ninety-nine percent of deaths in children under 5 years of age with influenza-related lower respiratory tract infections are in developing countries. […] Influenza A and B viruses circulate and cause seasonal epidemics of disease. […] Hospitalization and death due to influenza occur mainly among high-risk groups. […] The effects of seasonal influenza epidemics in developing countries are not fully known, but research estimates that 99% of deaths in children under 5 years of age with influenza related lower respiratory tract infections are in developing countries. […] People at greater risk of severe disease or complications when infected are pregnant women, children under 5 years of age, older people, individuals with chronic medical conditions and individuals with immunosuppressive conditions/treatments.

• #51

  https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)

  There are around a billion cases of seasonal influenza annually, including 35 million cases of severe illness. […] It causes 290 000 to 650 000 respiratory deaths annually. […] Ninety-nine percent of deaths in children under 5 years of age with influenza-related lower respiratory tract infections are in developing countries. […] Influenza A and B viruses circulate and cause seasonal epidemics of disease. […] Hospitalization and death due to influenza occur mainly among high-risk groups. […] The effects of seasonal influenza epidemics in developing countries are not fully known, but research estimates that 99% of deaths in children under 5 years of age with influenza related lower respiratory tract infections are in developing countries. […] People at greater risk of severe disease or complications when infected are pregnant women, children under 5 years of age, older people, individuals with chronic medical conditions and individuals with immunosuppressive conditions/treatments.

• #52 Human Influenza Epidemiology

  https://pmc.ncbi.nlm.nih.gov/articles/PMC8634793/

  One of the key determinants of the incidence of an influenza strain is its transmissibility, or its propensity to spread in a population. […] Influenza epidemics and pandemics can have considerable morbidity and mortality impact. […] Seasonal influenza tends to be associated with a substantial morbidity and mortality impact in older adults and those with underlying medical conditions. […] Influenza vaccines are the best available intervention to reduce the public health impact of influenza epidemics and pandemics. […] Nonpharmaceutical interventions (NPIs) also have an important role in mitigating influenza epidemics and pandemics in the community.

• #53

  https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)

  Epidemics can result in high levels of worker/school absenteeism and productivity losses. […] Seasonal influenza spreads easily, with rapid transmission in crowded areas including schools and nursing homes. […] The WHO Global Influenza Surveillance and Response System (GISRS) monitors resistance to antivirals among circulating influenza viruses to provide timely evidence for national policies related to antiviral use. […] Vaccination is the best way to prevent influenza. […] Vaccination is especially important for people at high risk of influenza complications and their carers. […] WHO, through the Global Influenza Programme and GISRS, in collaboration with other partners, continuously monitors influenza viruses and activity globally.

• #54

  https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)

  Epidemics can result in high levels of worker/school absenteeism and productivity losses. […] Seasonal influenza spreads easily, with rapid transmission in crowded areas including schools and nursing homes. […] The WHO Global Influenza Surveillance and Response System (GISRS) monitors resistance to antivirals among circulating influenza viruses to provide timely evidence for national policies related to antiviral use. […] Vaccination is the best way to prevent influenza. […] Vaccination is especially important for people at high risk of influenza complications and their carers. […] WHO, through the Global Influenza Programme and GISRS, in collaboration with other partners, continuously monitors influenza viruses and activity globally.

• #55 Azthena logo with the word Azthena

  https://www.news-medical.net/health/Influenza-Epidemiology.aspx

  Influenza virus is transmitted among humans in three main ways: by direct contact with infected individuals, through contaminated objects (such as hairbrushes or towels often called fomites) and by inhaling virus-laden aerosols. […] Nasal secretions that contain virus particles are responsible for transmission by direct contact or via contaminated objects. An infected individual most often touches the nose or conjunctiva, thus placing the virus on the hand. […] Researchers have shown that up to 60% of objects from homes and daycare facilities were shown to harbor influenza viral RNA. Infectious influenza virus may also persist on paper bills for several weeks, which is another possible way of spread. […] The epidemics caused by the influenza virus are estimated to result in about 3 to 5 million cases of severe illness, and up to 500 thousand deaths worldwide.

• #56 Azthena logo with the word Azthena

  https://www.news-medical.net/health/Influenza-Epidemiology.aspx

  Influenza virus is transmitted among humans in three main ways: by direct contact with infected individuals, through contaminated objects (such as hairbrushes or towels often called fomites) and by inhaling virus-laden aerosols. […] Nasal secretions that contain virus particles are responsible for transmission by direct contact or via contaminated objects. An infected individual most often touches the nose or conjunctiva, thus placing the virus on the hand. […] Researchers have shown that up to 60% of objects from homes and daycare facilities were shown to harbor influenza viral RNA. Infectious influenza virus may also persist on paper bills for several weeks, which is another possible way of spread. […] The epidemics caused by the influenza virus are estimated to result in about 3 to 5 million cases of severe illness, and up to 500 thousand deaths worldwide.

• #57 Influenza (Flu)

  https://dph.illinois.gov/topics-services/diseases-and-conditions/respiratory-disease/diseases/influenza.html

  Influenza viruses are divided into three types, designated A, B, and C. Influenza types A and B are responsible for epidemics of respiratory illness that occur almost every winter and are often associated with increased rates for hospitalization and death. […] Efforts to control the impact of influenza are aimed at types A and B. […] The flu is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness and, at times, can lead to death. […] While getting a flu vaccine each year is the best way to protect against flu, influenza antiviral drugs can fight against influenza, offering a second line of defense. […] Antiviral drugs are an important second line of defense against the flu. […] There are four FDA-approved antiviral drugs recommended by the Centers for Disease Control and Prevention (CDC) to treat flu this season.

• #58 Influenza (Flu)

  https://dph.illinois.gov/topics-services/diseases-and-conditions/respiratory-disease/diseases/influenza.html

  Influenza viruses are divided into three types, designated A, B, and C. Influenza types A and B are responsible for epidemics of respiratory illness that occur almost every winter and are often associated with increased rates for hospitalization and death. […] Efforts to control the impact of influenza are aimed at types A and B. […] The flu is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness and, at times, can lead to death. […] While getting a flu vaccine each year is the best way to protect against flu, influenza antiviral drugs can fight against influenza, offering a second line of defense. […] Antiviral drugs are an important second line of defense against the flu. […] There are four FDA-approved antiviral drugs recommended by the Centers for Disease Control and Prevention (CDC) to treat flu this season.

• #59

  https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)

  There are around a billion cases of seasonal influenza annually, including 35 million cases of severe illness. […] It causes 290 000 to 650 000 respiratory deaths annually. […] Ninety-nine percent of deaths in children under 5 years of age with influenza-related lower respiratory tract infections are in developing countries. […] Influenza A and B viruses circulate and cause seasonal epidemics of disease. […] Hospitalization and death due to influenza occur mainly among high-risk groups. […] The effects of seasonal influenza epidemics in developing countries are not fully known, but research estimates that 99% of deaths in children under 5 years of age with influenza related lower respiratory tract infections are in developing countries. […] People at greater risk of severe disease or complications when infected are pregnant women, children under 5 years of age, older people, individuals with chronic medical conditions and individuals with immunosuppressive conditions/treatments.

• #60 Azthena logo with the word Azthena

  https://www.news-medical.net/health/Influenza-Epidemiology.aspx

  Influenza is a highly infectious viral disease that can occur as a pandemic, epidemic, outbreak and in form of sporadic cases. A majority of human infections are caused by either type A or B influenza viruses. Type A has been associated with widespread epidemics and pandemics, while type B has been infrequently implicated in regional epidemics. Influenza type C infections cause only a mild respiratory illness. […] Yearly influenza epidemics can affect all populations, but children younger than the age of two, adults older than 65, as well as people with chronic medical conditions or weakened immune systems, bear the highest risk of complications. The annual attack rate is estimated at 510% in adults and 2030% in children. […] The epidemics caused by the influenza virus are estimated to result in about 3 to 5 million cases of severe illness, and up to 500 thousand deaths worldwide.

• #61 Weekly US Influenza Surveillance Report: Key Updates for Week 17, ending April 26, 2025 | FluView | CDC

  https://www.cdc.gov/fluview/surveillance/2025-week-17.html

  Seasonal influenza activity continues to decline. […] This season is classified as a high severity season overall and for all age groups (children, adults, older adults) and is the first high severity season since 2017-2018. […] During Week 17, of the 347 viruses reported by public health laboratories, 240 were influenza A and 107 were influenza B. Of the 200 influenza A viruses subtyped during Week 17, 135 (67.5%) were influenza A(H1N1)pdm09, 65 (32.5%) were A(H3N2), and 0 were A(H5). […] No new influenza A(H5) cases were reported to CDC this week. To date, human-to-human transmission of avian influenza A(H5) virus (H5 bird flu) has not been identified in the United States. […] Based on data from FluSurv-NET, the cumulative hospitalization rate for this season is the highest observed since the 2010-2011 season.

• #62 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  This includes genetic and antigenic characterization. […] The goals of genetic and antigenic characterization are to assess how similar the currently circulating influenza viruses are to viruses used to produce current influenza vaccines and to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. […] CDC also analyzes influenza viruses collected by public health laboratories for susceptibility to influenza antivirals, including neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and a PA cap-dependent endonuclease inhibitor (baloxavir). […] In 2007, human infection with a novel influenza A virus became a nationally notifiable condition in the United States. […] Rapid detection and reporting of human infections with novel influenza A viruses viruses against which there is often little to no pre-existing immunity in the population is important to facilitate prompt awareness and characterization of influenza A viruses with pandemic potential and accelerate the implementation of public health responses to limit the transmission and impact of these viruses.

• #63 WHO EMRO | Influenza surveillance | Influenza | Health topics

  https://www.emro.who.int/health-topics/influenza/influenza-surveillance.html

  The WHOs Global Influenza Programme (GIP) provides global standards for influenza surveillance. In addition, GIP collects and analyses virological and epidemiological influenza surveillance data from around the world. […] The regular sharing of quality influenza surveillance and monitoring data by countries allows WHO to: […] describe critical features of influenza epidemiology, including risk groups, transmission characteristics, and impact; […] monitor global trends in influenza transmission; and […] support the selection of influenza strains for vaccine production. […] Due to the constant evolving nature of influenza viruses, the WHO Global Influenza Surveillance and Response System (GISRS) a system of national influenza centres and WHO collaborating centres around the world continuously monitors the influenza viruses circulating in humans and updates the composition of influenza vaccines twice a year. […] The mission of GISRS is to protect people from the threat of influenza by continuously functioning as a: […] global mechanism of surveillance, preparedness and response for seasonal, pandemic and zoonotic influenza; […] global platform for monitoring influenza epidemiology and disease; and […] global alert for novel influenza viruses and other respiratory pathogens.

• #64 Influenza: epidemiology and hospital management

  https://pmc.ncbi.nlm.nih.gov/articles/PMC8624711/

  To date, the only influenza pandemic in the 21st century occurred between 2009 and 2010, caused by the A(H1N1)pdm09 virus and commonly known as swine flu. […] More than 214 countries were affected, with 284,000 deaths, of which 18,449 were laboratory confirmed. […] The WHO convenes consultations in February and September to recommend which strains to include in the vaccines for the Northern and Southern Hemispheres that are developed each year. […] Vaccination against influenza will be important in 202122 as the lack of circulation of influenza during 202021 will likely result in a reduced influenza global immunity. […] In the UK, influenza is a notifiable disease, and it is a statutory duty to report suspected disease to the proper officer at the local council or local health protection team.

• #65 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  This includes genetic and antigenic characterization. […] The goals of genetic and antigenic characterization are to assess how similar the currently circulating influenza viruses are to viruses used to produce current influenza vaccines and to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. […] CDC also analyzes influenza viruses collected by public health laboratories for susceptibility to influenza antivirals, including neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and a PA cap-dependent endonuclease inhibitor (baloxavir). […] In 2007, human infection with a novel influenza A virus became a nationally notifiable condition in the United States. […] Rapid detection and reporting of human infections with novel influenza A viruses viruses against which there is often little to no pre-existing immunity in the population is important to facilitate prompt awareness and characterization of influenza A viruses with pandemic potential and accelerate the implementation of public health responses to limit the transmission and impact of these viruses.

• #66

  https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)

  Epidemics can result in high levels of worker/school absenteeism and productivity losses. […] Seasonal influenza spreads easily, with rapid transmission in crowded areas including schools and nursing homes. […] The WHO Global Influenza Surveillance and Response System (GISRS) monitors resistance to antivirals among circulating influenza viruses to provide timely evidence for national policies related to antiviral use. […] Vaccination is the best way to prevent influenza. […] Vaccination is especially important for people at high risk of influenza complications and their carers. […] WHO, through the Global Influenza Programme and GISRS, in collaboration with other partners, continuously monitors influenza viruses and activity globally.

• #67 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  This includes genetic and antigenic characterization. […] The goals of genetic and antigenic characterization are to assess how similar the currently circulating influenza viruses are to viruses used to produce current influenza vaccines and to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. […] CDC also analyzes influenza viruses collected by public health laboratories for susceptibility to influenza antivirals, including neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and a PA cap-dependent endonuclease inhibitor (baloxavir). […] In 2007, human infection with a novel influenza A virus became a nationally notifiable condition in the United States. […] Rapid detection and reporting of human infections with novel influenza A viruses viruses against which there is often little to no pre-existing immunity in the population is important to facilitate prompt awareness and characterization of influenza A viruses with pandemic potential and accelerate the implementation of public health responses to limit the transmission and impact of these viruses.

• #68 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  This includes genetic and antigenic characterization. […] The goals of genetic and antigenic characterization are to assess how similar the currently circulating influenza viruses are to viruses used to produce current influenza vaccines and to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. […] CDC also analyzes influenza viruses collected by public health laboratories for susceptibility to influenza antivirals, including neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and a PA cap-dependent endonuclease inhibitor (baloxavir). […] In 2007, human infection with a novel influenza A virus became a nationally notifiable condition in the United States. […] Rapid detection and reporting of human infections with novel influenza A viruses viruses against which there is often little to no pre-existing immunity in the population is important to facilitate prompt awareness and characterization of influenza A viruses with pandemic potential and accelerate the implementation of public health responses to limit the transmission and impact of these viruses.

• #69 Influenza – Wikipedia

  https://en.wikipedia.org/wiki/Influenza

  Influenza A virus and influenza B virus co-circulate, so have the same patterns of transmission. […] Outbreaks of influenza caused by novel influenza viruses are common. […] Depending on the level of pre-existing immunity in the population, novel influenza viruses can spread rapidly and cause pandemics with millions of deaths. […] These pandemics, in contrast to seasonal influenza, are caused by antigenic shifts involving animal influenza viruses. […] To date, all known flu pandemics have been caused by influenza A viruses, and they follow the same pattern of spreading from an origin point to the rest of the world over the course of multiple waves in a year.

• #70 Influenza – Wikipedia

  https://en.wikipedia.org/wiki/Influenza

  Influenza A virus and influenza B virus co-circulate, so have the same patterns of transmission. […] Outbreaks of influenza caused by novel influenza viruses are common. […] Depending on the level of pre-existing immunity in the population, novel influenza viruses can spread rapidly and cause pandemics with millions of deaths. […] These pandemics, in contrast to seasonal influenza, are caused by antigenic shifts involving animal influenza viruses. […] To date, all known flu pandemics have been caused by influenza A viruses, and they follow the same pattern of spreading from an origin point to the rest of the world over the course of multiple waves in a year.

• #71 Influenza – Wikipedia

  https://en.wikipedia.org/wiki/Influenza

  Influenza A virus and influenza B virus co-circulate, so have the same patterns of transmission. […] Outbreaks of influenza caused by novel influenza viruses are common. […] Depending on the level of pre-existing immunity in the population, novel influenza viruses can spread rapidly and cause pandemics with millions of deaths. […] These pandemics, in contrast to seasonal influenza, are caused by antigenic shifts involving animal influenza viruses. […] To date, all known flu pandemics have been caused by influenza A viruses, and they follow the same pattern of spreading from an origin point to the rest of the world over the course of multiple waves in a year.

• #72 Epidemiological and virological surveillance of influenza viruses in China during 2020–2021 | Infectious Diseases of Poverty | Full Text

  https://idpjournal.biomedcentral.com/articles/10.1186/s40249-022-01002-x

  During the coronavirus disease 2019 (COVID-19) pandemic, seasonal influenza activity declined globally and remained below previous seasonal levels, but intensified in China since 2021. […] To better respond to influenza outbreaks under the COVID-19 pandemic, we analyzed the epidemiology, antigenic and genetic characteristics, and antiviral susceptibility of influenza viruses in the mainland of China during 20202021. […] In the mainland of China, influenza activity recovered in 2021 compared with that in 2020 and intensified during the traditional influenza winter season, but it did not exceed the peak in previous years. […] 37.8% viruses tested were antigenically similar to reference viruses representing the components of the vaccine for the 20202021 and 20212022 Northern Hemisphere influenza seasons.

• #73 Influenza: epidemiology and hospital management

  https://pmc.ncbi.nlm.nih.gov/articles/PMC8624711/

  Innovative technologies, new pharmaceuticals and improved global surveillance are changing the way healthcare systems respond to influenza and other diseases to ensure global health resilience and effective management of future outbreaks. […] Seasonal influenza is a common cause of respiratory infection during the winter months in Northern and Southern Hemispheres, and can occur all year round in tropical and subtropical areas. […] Annual seasonal influenza epidemics result in around 290,000650,000 deaths worldwide and infect up to 20% of the population, depending on circulating viral strains. […] At the time of writing, there are reduced levels of influenza globally compared with previous years, probably secondary to the non-pharmacological interventions (social distancing, hand hygiene) implemented to reduce severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission.

• #74 Epidemiological and virological surveillance of influenza viruses in China during 2020–2021 | Infectious Diseases of Poverty | Full Text

  https://idpjournal.biomedcentral.com/articles/10.1186/s40249-022-01002-x

  During the coronavirus disease 2019 (COVID-19) pandemic, seasonal influenza activity declined globally and remained below previous seasonal levels, but intensified in China since 2021. […] To better respond to influenza outbreaks under the COVID-19 pandemic, we analyzed the epidemiology, antigenic and genetic characteristics, and antiviral susceptibility of influenza viruses in the mainland of China during 20202021. […] In the mainland of China, influenza activity recovered in 2021 compared with that in 2020 and intensified during the traditional influenza winter season, but it did not exceed the peak in previous years. […] 37.8% viruses tested were antigenically similar to reference viruses representing the components of the vaccine for the 20202021 and 20212022 Northern Hemisphere influenza seasons.

• #75 Epidemiological and virological surveillance of influenza viruses in China during 2020–2021 | Infectious Diseases of Poverty | Full Text

  https://idpjournal.biomedcentral.com/articles/10.1186/s40249-022-01002-x

  Influenza activity increased in the mainland of China in 2021, and caused flu season in the winter of 20212022. […] The world needs to be fully prepared for the co-epidemic of influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus globally. […] Influenza imposes a significant disease burden on the global population. […] Annual influenza vaccination is the main option for the prevention and control of influenza viruses. […] In 2021, SARS-CoV-2 continued to circulate globally, however, influenza epidemics were reported by a number of countries and regions, with higher detections of influenza activity in 20212022 winter season than in 20202021 season, particularly in Europe, North America, Africa and China. […] Compared to previous seasons, the diversity of (sub)type of influenza virus co-circulating has decreased in China since COVID-19, with nearly all of them are B/Victoria lineage viruses.

• #76 Weekly US Influenza Surveillance Report: Key Updates for Week 17, ending April 26, 2025 | FluView | CDC

  https://www.cdc.gov/fluview/surveillance/2025-week-17.html

  CDC estimates that there have been at least 47 million illnesses, 610,000 hospitalizations, and 26,000 deaths from flu so far this season. […] CDC continues to recommend that everyone ages 6 months and older get an annual flu vaccine as long as influenza viruses are circulating. […] There are prescription flu antiviral drugs that can treat flu illness; those should be started as early as possible and are especially important for patients at higher risk for severe illness. […] Influenza viruses are among several viruses contributing to respiratory disease activity. CDC is providing updated, integrated information about COVID-19, flu, and respiratory syncytial virus (RSV) activity on a weekly basis. […] The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in 14 states and represents approximately 9% of the U.S. population.

• #77 Chicago Department of Public Health

  https://www.chicago.gov/city/en/depts/cdph/supp_info/infectious/respiratory-illness/historical-respiratory-virus-surveillance-reports.html

  The Chicago Department of Public Health provides weekly reports that detail the current flu risk, which influenza strains are circulating, and where can you get more information. […] Beginning in December 2021, CDPH expanded laboratory surveillance to include other respiratory viruses besides influenza; the updated report is now called the Chicago Influenza and Respiratory Virus Surveillance Report.

• #78 Influenza: epidemiology and hospital management

  https://pmc.ncbi.nlm.nih.gov/articles/PMC8624711/

  Influenza is a cause of significant morbidity, mortality, economic and social disruption. Annual seasonal influenza epidemics result in 290,000650,000 deaths worldwide, while influenza pandemics have resulted in many more the A(H1N1) pandemic of 19181919 caused 2050 million deaths. […] Since the start of 2021, there have been four events of concern related to influenza reported by the World Health Organization. […] To reduce the burden of disease and protect our global health security, it is essential that clinicians effectively identify and manage cases of influenza, as well as understand and collaborate with the wider public and global health systems. […] In particular, the rapid identification and management of novel influenza strains of concern is critical. […] The COVID-19 pandemic has instigated improvements in influenza preparedness guidelines and management protocols.

• #79 Influenza: epidemiology and hospital management

  https://pmc.ncbi.nlm.nih.gov/articles/PMC8624711/

  Innovative technologies, new pharmaceuticals and improved global surveillance are changing the way healthcare systems respond to influenza and other diseases to ensure global health resilience and effective management of future outbreaks. […] Seasonal influenza is a common cause of respiratory infection during the winter months in Northern and Southern Hemispheres, and can occur all year round in tropical and subtropical areas. […] Annual seasonal influenza epidemics result in around 290,000650,000 deaths worldwide and infect up to 20% of the population, depending on circulating viral strains. […] At the time of writing, there are reduced levels of influenza globally compared with previous years, probably secondary to the non-pharmacological interventions (social distancing, hand hygiene) implemented to reduce severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission.

• #80 Epidemiological and virological surveillance of influenza viruses in China during 2020–2021 | Infectious Diseases of Poverty | Full Text

  https://idpjournal.biomedcentral.com/articles/10.1186/s40249-022-01002-x

  The surveillance data presented here remind us that influenza activity is recovering in 2021, although not yet reached the highest level before COVID-19 pandemic. […] Influenza surveillance should be continuously strengthened, and there is an urgent need to make full preparations for the co-epidemic of influenza and SARS-CoV-2 virus globally.

• #81 Influenza: epidemiology and hospital management

  https://pmc.ncbi.nlm.nih.gov/articles/PMC8624711/

  To date, the only influenza pandemic in the 21st century occurred between 2009 and 2010, caused by the A(H1N1)pdm09 virus and commonly known as swine flu. […] More than 214 countries were affected, with 284,000 deaths, of which 18,449 were laboratory confirmed. […] The WHO convenes consultations in February and September to recommend which strains to include in the vaccines for the Northern and Southern Hemispheres that are developed each year. […] Vaccination against influenza will be important in 202122 as the lack of circulation of influenza during 202021 will likely result in a reduced influenza global immunity. […] In the UK, influenza is a notifiable disease, and it is a statutory duty to report suspected disease to the proper officer at the local council or local health protection team.

• #82

  https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)

  Epidemics can result in high levels of worker/school absenteeism and productivity losses. […] Seasonal influenza spreads easily, with rapid transmission in crowded areas including schools and nursing homes. […] The WHO Global Influenza Surveillance and Response System (GISRS) monitors resistance to antivirals among circulating influenza viruses to provide timely evidence for national policies related to antiviral use. […] Vaccination is the best way to prevent influenza. […] Vaccination is especially important for people at high risk of influenza complications and their carers. […] WHO, through the Global Influenza Programme and GISRS, in collaboration with other partners, continuously monitors influenza viruses and activity globally.

• #83

  https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)

  Epidemics can result in high levels of worker/school absenteeism and productivity losses. […] Seasonal influenza spreads easily, with rapid transmission in crowded areas including schools and nursing homes. […] The WHO Global Influenza Surveillance and Response System (GISRS) monitors resistance to antivirals among circulating influenza viruses to provide timely evidence for national policies related to antiviral use. […] Vaccination is the best way to prevent influenza. […] Vaccination is especially important for people at high risk of influenza complications and their carers. […] WHO, through the Global Influenza Programme and GISRS, in collaboration with other partners, continuously monitors influenza viruses and activity globally.

• #84

  https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)

  Epidemics can result in high levels of worker/school absenteeism and productivity losses. […] Seasonal influenza spreads easily, with rapid transmission in crowded areas including schools and nursing homes. […] The WHO Global Influenza Surveillance and Response System (GISRS) monitors resistance to antivirals among circulating influenza viruses to provide timely evidence for national policies related to antiviral use. […] Vaccination is the best way to prevent influenza. […] Vaccination is especially important for people at high risk of influenza complications and their carers. […] WHO, through the Global Influenza Programme and GISRS, in collaboration with other partners, continuously monitors influenza viruses and activity globally.

• #85 Influenza (Flu) – Epidemiology

  https://www.vdh.virginia.gov/epidemiology/epidemiology-fact-sheets/influenza/

  Yes. It is important to get vaccinated for flu every year. The flu vaccine formulation changes year to year to best match the flu viruses research indicates will be most common during the upcoming season. Also, protection from the flu vaccine decreases over time, so getting a flu vaccine every year will give you the best protection.

• #86 U.S. Influenza Surveillance: Purpose and Methods | FluView | CDC

  https://www.cdc.gov/fluview/overview/index.html

  It is important to maintain a comprehensive system for influenza surveillance for the following reasons: Influenza viruses are constantly undergoing minor changes (this is commonly referred to as „antigenic drift”), and ongoing data collection and characterization of viruses helps to monitor these changes. […] Surveillance of viruses can detect these changes and help inform the public health response. […] Annual vaccination is recommended, and vaccines are updated regularly based on surveillance findings. […] Treatment recommendations for influenza virus infection are informed by laboratory surveillance for antiviral resistance. […] Influenza surveillance and targeted research studies are used to monitor the impact of influenza on different segments of the population (e.g., people in certain age groups, people with underlying medical conditions) and the impact of influenza prevention measures such as vaccines.

• #87

  https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)

  Epidemics can result in high levels of worker/school absenteeism and productivity losses. […] Seasonal influenza spreads easily, with rapid transmission in crowded areas including schools and nursing homes. […] The WHO Global Influenza Surveillance and Response System (GISRS) monitors resistance to antivirals among circulating influenza viruses to provide timely evidence for national policies related to antiviral use. […] Vaccination is the best way to prevent influenza. […] Vaccination is especially important for people at high risk of influenza complications and their carers. […] WHO, through the Global Influenza Programme and GISRS, in collaboration with other partners, continuously monitors influenza viruses and activity globally.

• #88 Influenza (Flu) – Epidemiology

  https://www.vdh.virginia.gov/epidemiology/epidemiology-fact-sheets/influenza/

  Prescription antiviral medications are available to people who are very sick with flu or at increased risk of developing serious flu complications. These treatments can reduce the severity of flu and shorten the time someone is sick. They work best when started within one to two days after symptoms begin. […] Close contacts of a person with flu might want to contact their healthcare provider or seek medical evaluation for vaccination, testing, or antiviral medication to prevent flu. […] Getting a flu vaccine every year is the most important action you can take to prevent the flu. […] Everyone aged six months or older, with rare exceptions, should get a flu vaccine each year. Vaccination is especially important for people who are at higher risk of developing serious flu complications.

• #89 Influenza (Flu) – Epidemiology

  https://www.vdh.virginia.gov/epidemiology/epidemiology-fact-sheets/influenza/

  Prescription antiviral medications are available to people who are very sick with flu or at increased risk of developing serious flu complications. These treatments can reduce the severity of flu and shorten the time someone is sick. They work best when started within one to two days after symptoms begin. […] Close contacts of a person with flu might want to contact their healthcare provider or seek medical evaluation for vaccination, testing, or antiviral medication to prevent flu. […] Getting a flu vaccine every year is the most important action you can take to prevent the flu. […] Everyone aged six months or older, with rare exceptions, should get a flu vaccine each year. Vaccination is especially important for people who are at higher risk of developing serious flu complications.

• #90 Influenza | MeCDC | Maine DHHS

  https://www.maine.gov/dhhs/mecdc/infectious-disease/epi/influenza/maineflu/

  Influenza (flu) is a contagious respiratory illness caused by viruses that infect the nose, throat, and lungs. Some people are at higher risk of serious complications due to influenza. There are two main types of influenza viruses: Types A and B. The influenza A and B viruses that routinely spread in people (human influenza viruses) are responsible for seasonal epidemics each year. […] Surveillance Reports […] Schools should report when they reach = 15% absenteeism due to illness. Reporting should occur through NEO. […] If an outbreak is suspected (two or more residents develop respiratory illness within 72 hours of each other): Report the outbreak to Maine CDC via phone at 1-800-821-5821 or email at [email protected]. […] Infection preventionists, clinicians, school nurses, and other reporting entities must report all suspected outbreaks of flu to Maine CDC by phone at 1-800-821-5821 or email [email protected].

• #91 Human Influenza Epidemiology

  https://pmc.ncbi.nlm.nih.gov/articles/PMC8634793/

  One of the key determinants of the incidence of an influenza strain is its transmissibility, or its propensity to spread in a population. […] Influenza epidemics and pandemics can have considerable morbidity and mortality impact. […] Seasonal influenza tends to be associated with a substantial morbidity and mortality impact in older adults and those with underlying medical conditions. […] Influenza vaccines are the best available intervention to reduce the public health impact of influenza epidemics and pandemics. […] Nonpharmaceutical interventions (NPIs) also have an important role in mitigating influenza epidemics and pandemics in the community.

• #92 Influenza: epidemiology and hospital management

  https://pmc.ncbi.nlm.nih.gov/articles/PMC8624711/

  Innovative technologies, new pharmaceuticals and improved global surveillance are changing the way healthcare systems respond to influenza and other diseases to ensure global health resilience and effective management of future outbreaks. […] Seasonal influenza is a common cause of respiratory infection during the winter months in Northern and Southern Hemispheres, and can occur all year round in tropical and subtropical areas. […] Annual seasonal influenza epidemics result in around 290,000650,000 deaths worldwide and infect up to 20% of the population, depending on circulating viral strains. […] At the time of writing, there are reduced levels of influenza globally compared with previous years, probably secondary to the non-pharmacological interventions (social distancing, hand hygiene) implemented to reduce severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission.

• #93 Overview of Influenza Surveillance in the United States | Seasonal Influenza (Flu) | CDC

  http://medbox.iiab.me/modules/en-cdc/espanol.cdc.gov/enes/flu/weekly/overview.htm

  The Epidemiology and Prevention Branch in the Influenza Division at CDC collects, compiles and analyzes information on influenza activity year-round in the United States and produces FluView, a weekly influenza surveillance report, and FluView Interactive, which allows for more in-depth exploration of influenza surveillance data. […] The U.S. influenza surveillance system is a collaborative effort between CDC and its many partners in state, local, and territorial health departments, public health and clinical laboratories, vital statistics offices, healthcare providers, clinics, and emergency departments. […] Information in five categories is collected from eight different data sources that allows CDC to: Find out when and where influenza activity is occurring, Track influenza-related illness, Determine what influenza viruses are circulating, Detect changes in influenza viruses, Measure the impact influenza is having on hospitalizations and deaths.

• #94 Influenza Activity, Surveillance and Reports – New York State Department of Health

  https://www.health.ny.gov/diseases/communicable/influenza/surveillance/

  The New York State Department of Health (NYSDOH) collects, compiles, and analyzes information on flu activity year-round in New York State (NYS), and produces a weekly report during the flu season (October through the following May). […] In view of persisting elevated influenza activity throughout NYS, NYSDOH is extending the surveillance season beyond May until influenza activity has decreased.

• #95 Weekly Influenza and Respiratory Activity: Statistics – MN Dept. of Health

  https://www.health.state.mn.us/diseases/flu/stats/index.html

  Influenza Respiratory Illness Activity Report – Week 18 (PDF)Week Ending May 3, 2025 | WEEK 18 […] Unlike other reportable diseases, MDH does not request that every case of influenza or every patient who goes to the doctor with influenza symptoms be reported to MDH. Tracking each case would overburden health care providers as well as MDH, without significant benefit. Instead, MDH uses several different surveillance programs to determine the burden of influenza disease in Minnesota each week (influenza-like illness [ILI] outbreaks at schools and long-term care facilities, outpatient/clinic visits for ILI, laboratory-confirmed influenza in hospitalized patients, and laboratory testing for influenza and other respiratory disease). […] Many people get sick with flu every year in Minnesota without ever seeing a doctor or reporting their illness. Therefore, MDH uses various indicators to find out how widespread the flu is in Minnesota each week, rather than trying to track every case. The MDH Public Health Laboratory (PHL) also tests selected influenza specimens to monitor which flu strains are circulating each flu season.

• #96 Influenza: Practice Essentials, Background, Pathophysiology

  https://emedicine.medscape.com/article/219557-overview

  Influenza, one of the most common infectious diseases, is a highly contagious airborne disease that occurs in seasonal epidemics and manifests as an acute febrile illness with variable degrees of systemic symptoms, ranging from mild fatigue to respiratory failure and death. Influenza causes significant loss of workdays, human suffering, and mortality. […] The WHO estimates that 1 billion influenza cases, 3 to 5 million severe cases, and 290,000 to 650,000 influenza-related respiratory deaths occur each year worldwide. […] In the United States, individual cases of seasonal flu and flu-related deaths in adults are not reportable illnesses; consequently, mortality is estimated by using statistical models. […] The CDC estimates that flu-associated deaths in the United States ranged from about 3000 to 49,000 annually between 1976 and 2006.

• #97 Influenza: Practice Essentials, Background, Pathophysiology

  https://emedicine.medscape.com/article/219557-overview

  Unlike adult flu-related deaths, pediatric flu-related deaths are reportable in the United States. […] For the 2019-2020 influenza season, the CDC reports an estimated 35 million influenza-associated illnesses, 16 million influenza-related medical visits, 380,000 flu-associated hospitalizations, and 20,000 influenza-related deaths. […] The 1918 H1N1 influenza pandemic caused 500,000-700,000 deaths in the United Statesalmost 200,000 of them in October 1918 aloneand an estimated 30-40 million deaths worldwide, mostly among people aged 15-35 years. […] The 2009-2010 influenza season was affected by the H1N1 (swine flu) influenza epidemic, the first wave of which hit the United States in the spring of 2009, followed by a second, larger wave in the fall and winter; activity peaked in October and then quickly declined to below baseline levels by January 2010.

• #98 European Influenza Surveillance Network (EISN)

  https://www.ecdc.europa.eu/en/about-us/partnerships-and-networks/disease-and-laboratory-networks/eisn

  The European Influenza Surveillance Network (EISN) is coordinated by ECDC. The network combines epidemiological and virological surveillance of influenza to provide decision makers and public health experts in EU/EEA Member States with the information required to better assess influenza activity in Europe and take appropriate action. Ultimately, EISN aims to contribute to reducing the burden of disease associated with influenza in Europe. […] Virological surveillance activities are coordinated through the European Reference Laboratory Network for Human Influenza (ERLI-Net), a sub-network within EISN. […] The following epidemiological and virological influenza surveillance data are collected through The European Surveillance System (TESSy) database hosted by ECDC: […] On an operational level, EISN consists of operational contact points for influenza epidemiology and virology.

• #99 Surveillance for seasonal influenza

  https://www.ecdc.europa.eu/en/seasonal-influenza/surveillance-reports-and-disease-data

  ECDC collects epidemiological and virological data from the EU/EEA Member States. The surveillance data reported comes largely from sentinel influenza surveillance systems, which cover a subset of the population in each country. […] Several countries also conduct surveillance of hospitalised cases. A sample of cases is also tested to determine virus characteristics. […] The weekly surveillance of seasonal influenza is complemented by epidemic intelligence activities at ECDC, which encompass monitoring of official and unofficial sources on outbreaks and other influenza-related developments. […] ECDCs influenza virus characterisation reports are published periodically and give an overview of circulating influenza viruses. They provide details on the current vaccine strains, summarise the development of the viruses since the last report, and closely follow the main developments for the ongoing influenza season.

• #100 Surveillance for seasonal influenza

  https://www.ecdc.europa.eu/en/seasonal-influenza/surveillance-reports-and-disease-data

  The specific goal of influenza surveillance is to provide timely and high-quality data and viral isolates. […] The clinical surveillance of influenza in the European Influenza Surveillance Network (EISN) is generally based on reports made by sentinel general practitioners. […] The Global Influenza Surveillance and Response System (GISRS), led by WHO, is used for the international virological and epidemiological surveillance of human influenza. […] The network combines epidemiological and virological surveillance of influenza.

• #101

  https://link.springer.com/article/10.1007/s40121-021-00534-3

  Seasonal influenza represents a huge health burden, resulting in significant mortality and morbidity. […] Despite improvements in influenza surveillance following the 2009 pandemic, many opportunities remain unexplored in the Eastern Mediterranean and North African (EMNA) region, which has a high prevalence of patients with chronic disease and thus a population at high risk of influenza complications. […] Our review reveals existing gaps in regional estimates of influenza health and economic burden, hospitalisation rates and duration, and highlights the need for robust and high-quality epidemiology data to help inform public health interventions. […] The Eastern Mediterranean and North African (EMNA) region is geographically contiguous, making it an important region for influenza surveillance, yet the burden of disease is not well characterized in the region, and there are several countries with little to no data on influenza epidemiology.

• #102

  https://link.springer.com/article/10.1007/s40121-021-00534-3

  Seasonal influenza represents a huge health burden, resulting in significant mortality and morbidity. […] Despite improvements in influenza surveillance following the 2009 pandemic, many opportunities remain unexplored in the Eastern Mediterranean and North African (EMNA) region, which has a high prevalence of patients with chronic disease and thus a population at high risk of influenza complications. […] Our review reveals existing gaps in regional estimates of influenza health and economic burden, hospitalisation rates and duration, and highlights the need for robust and high-quality epidemiology data to help inform public health interventions. […] The Eastern Mediterranean and North African (EMNA) region is geographically contiguous, making it an important region for influenza surveillance, yet the burden of disease is not well characterized in the region, and there are several countries with little to no data on influenza epidemiology.

• #103

  https://link.springer.com/article/10.1007/s40121-021-00534-3

  The region has a high prevalence of patients with chronic disease and thus a population at high risk of seasonal influenza complications; hence, these data are essential in helping to inform decisions on national and regional influenza intervention programmes. […] The study highlighted important gaps in regional estimates of influenza health and economic burden, hospitalisation rates and duration of hospital stay and a lack of surveillance standardization for influenza across countries. […] There is a high need for robust and high-quality epidemiology data and strengthening of surveillance systems to help inform public health interventions in the EMNA region. […] Epidemiological and virological surveillance have been improved in the region since the formation of the Eastern Mediterranean Acute Respiratory Infection Surveillance (EMARIS) network, but is still far from well established, particularly as the network only collects data on severe respiratory infections, but not non-severe cases.

• #104 Epidemiological and virological surveillance of influenza viruses in China during 2020–2021 | Infectious Diseases of Poverty | Full Text

  https://idpjournal.biomedcentral.com/articles/10.1186/s40249-022-01002-x

  During the coronavirus disease 2019 (COVID-19) pandemic, seasonal influenza activity declined globally and remained below previous seasonal levels, but intensified in China since 2021. […] To better respond to influenza outbreaks under the COVID-19 pandemic, we analyzed the epidemiology, antigenic and genetic characteristics, and antiviral susceptibility of influenza viruses in the mainland of China during 20202021. […] In the mainland of China, influenza activity recovered in 2021 compared with that in 2020 and intensified during the traditional influenza winter season, but it did not exceed the peak in previous years. […] 37.8% viruses tested were antigenically similar to reference viruses representing the components of the vaccine for the 20202021 and 20212022 Northern Hemisphere influenza seasons.

• #105 Epidemiological and virological surveillance of influenza viruses in China during 2020–2021 | Infectious Diseases of Poverty | Full Text

  https://idpjournal.biomedcentral.com/articles/10.1186/s40249-022-01002-x

  Influenza activity increased in the mainland of China in 2021, and caused flu season in the winter of 20212022. […] The world needs to be fully prepared for the co-epidemic of influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus globally. […] Influenza imposes a significant disease burden on the global population. […] Annual influenza vaccination is the main option for the prevention and control of influenza viruses. […] In 2021, SARS-CoV-2 continued to circulate globally, however, influenza epidemics were reported by a number of countries and regions, with higher detections of influenza activity in 20212022 winter season than in 20202021 season, particularly in Europe, North America, Africa and China. […] Compared to previous seasons, the diversity of (sub)type of influenza virus co-circulating has decreased in China since COVID-19, with nearly all of them are B/Victoria lineage viruses.

• #106 Epidemiological and virological surveillance of influenza viruses in China during 2020–2021 | Infectious Diseases of Poverty | Full Text

  https://idpjournal.biomedcentral.com/articles/10.1186/s40249-022-01002-x

  Influenza activity increased in the mainland of China in 2021, and caused flu season in the winter of 20212022. […] The world needs to be fully prepared for the co-epidemic of influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus globally. […] Influenza imposes a significant disease burden on the global population. […] Annual influenza vaccination is the main option for the prevention and control of influenza viruses. […] In 2021, SARS-CoV-2 continued to circulate globally, however, influenza epidemics were reported by a number of countries and regions, with higher detections of influenza activity in 20212022 winter season than in 20202021 season, particularly in Europe, North America, Africa and China. […] Compared to previous seasons, the diversity of (sub)type of influenza virus co-circulating has decreased in China since COVID-19, with nearly all of them are B/Victoria lineage viruses.

• #107 Influenza – Wikipedia

  https://en.wikipedia.org/wiki/Influenza

  Influenza is typically characterized by seasonal epidemics and sporadic pandemics. […] Most of the burden of influenza is a result of flu seasons caused by influenza A virus and influenza B virus. […] In a typical year, influenza viruses infect 5-15% of the global population, causing 35 million cases of severe illness annually and accounting for 290,000-650,000 deaths each year due to respiratory illness. […] The reported number of influenza cases is usually much lower than the actual number. […] During seasonal epidemics, it is estimated that about 80% of otherwise healthy people who have a cough or sore throat have the flu. […] Approximately 30-40% of people hospitalized for influenza develop pneumonia, and about 5% of all severe pneumonia cases in hospitals are due to influenza, which is also the most common cause of ARDS in adults.

• #108

  https://link.springer.com/article/10.1007/s40121-021-00534-3

  The increase in the number of publications and research around influenza since the 2009 pandemic is encouraging and suggests an increase in awareness around influenza and the importance of reducing its burden. […] However, much work remains to be done. The heterogeneity in assessment and data collection across the region makes surveillance comparisons difficult. […] Our results highlight the need for robust and high-quality epidemiology data to inform policy and refine public health interventions.

• #109

  https://link.springer.com/article/10.1007/s40121-021-00534-3

  The increase in the number of publications and research around influenza since the 2009 pandemic is encouraging and suggests an increase in awareness around influenza and the importance of reducing its burden. […] However, much work remains to be done. The heterogeneity in assessment and data collection across the region makes surveillance comparisons difficult. […] Our results highlight the need for robust and high-quality epidemiology data to inform policy and refine public health interventions.

• #110 Department of Health | Communicable Disease Service | Influenza Illness Surveillance Reports

  https://www.nj.gov/health/cd/statistics/flu-stats/

  Influenza Surveillance Reports […] The new Respiratory Illness Surveillance Report, summarizing weekly data for COVID-19, influenza, RSV, and other respiratory illnesses, is available here. […] View the Influenza Illness Surveillance reports archive.

• #111 Influenza: epidemiology and hospital management

  https://pmc.ncbi.nlm.nih.gov/articles/PMC8624711/

  Innovative technologies, new pharmaceuticals and improved global surveillance are changing the way healthcare systems respond to influenza and other diseases to ensure global health resilience and effective management of future outbreaks. […] Seasonal influenza is a common cause of respiratory infection during the winter months in Northern and Southern Hemispheres, and can occur all year round in tropical and subtropical areas. […] Annual seasonal influenza epidemics result in around 290,000650,000 deaths worldwide and infect up to 20% of the population, depending on circulating viral strains. […] At the time of writing, there are reduced levels of influenza globally compared with previous years, probably secondary to the non-pharmacological interventions (social distancing, hand hygiene) implemented to reduce severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission.

• #112 Purple Death: The Great Flu of 1918 – PAHO/WHO | Pan American Health Organization

  https://www.paho.org/en/who-we-are/history-paho/purple-death-great-flu-1918

  Every year, the world catches a new influenza virus. […] However, as historical records dating from the 1700s show, every 10 to 40 years the world suffers a global flu pandemic, the result of a major antigenic drift. […] „History tells us we are ready for another pandemic,” says Kirsty Duncan, Spanish flu researcher and author of Hunting the 1918 Flu: One Scientist’s Search for a Killer Virus. […] He cites Taubenberger’s pioneering work in developing new techniques for analyzing genetic changes in influenza viruses.

• #113 Purple Death: The Great Flu of 1918 – PAHO/WHO | Pan American Health Organization

  https://www.paho.org/en/who-we-are/history-paho/purple-death-great-flu-1918

  Every year, the world catches a new influenza virus. […] However, as historical records dating from the 1700s show, every 10 to 40 years the world suffers a global flu pandemic, the result of a major antigenic drift. […] „History tells us we are ready for another pandemic,” says Kirsty Duncan, Spanish flu researcher and author of Hunting the 1918 Flu: One Scientist’s Search for a Killer Virus. […] He cites Taubenberger’s pioneering work in developing new techniques for analyzing genetic changes in influenza viruses.

• #114 Purple Death: The Great Flu of 1918 – PAHO/WHO | Pan American Health Organization

  https://www.paho.org/en/who-we-are/history-paho/purple-death-great-flu-1918

  Every year, the world catches a new influenza virus. […] However, as historical records dating from the 1700s show, every 10 to 40 years the world suffers a global flu pandemic, the result of a major antigenic drift. […] „History tells us we are ready for another pandemic,” says Kirsty Duncan, Spanish flu researcher and author of Hunting the 1918 Flu: One Scientist’s Search for a Killer Virus. […] He cites Taubenberger’s pioneering work in developing new techniques for analyzing genetic changes in influenza viruses.

• #115

  https://link.springer.com/article/10.1007/s40121-021-00534-3

  The increase in the number of publications and research around influenza since the 2009 pandemic is encouraging and suggests an increase in awareness around influenza and the importance of reducing its burden. […] However, much work remains to be done. The heterogeneity in assessment and data collection across the region makes surveillance comparisons difficult. […] Our results highlight the need for robust and high-quality epidemiology data to inform policy and refine public health interventions.

• #116 How severe is this flu season shaping up to be? | Doherty Website

  https://www.doherty.edu.au/news-events/news/how-severe-is-this-flu-season-shaping-up-to-be

  Australia has recorded an increased number of lab-confirmed influenza cases in all jurisdictions early in 2025, but we cant currently predict the severity of the upcoming season in Australia according to Professor Patrick Reading, Director of the WHO Collaborating Centre for Reference and Research on Influenza. […] Despite the increased influenza activity, we cant currently predict the severity of the upcoming season in Australia said Professor Reading. […] The WHO Global Influenza Surveillance and Response System monitors circulating virus strains worldwide and convenes biannual meetings to recommend candidate vaccine viruses for the upcoming flu seasons in each hemisphere. […] Professor Paul Griffin highlighted the severity of influenza compared to other viral respiratory infections and discussed the best preventative and treatment measures. […] Its always a bad flu season because its hospitalising and killing people and making them sickit doesnt necessarily need to be a record flu season for it to be important, said Professor Leask.

• #117 How severe is this flu season shaping up to be? | Doherty Website

  https://www.doherty.edu.au/news-events/news/how-severe-is-this-flu-season-shaping-up-to-be

  Australia has recorded an increased number of lab-confirmed influenza cases in all jurisdictions early in 2025, but we cant currently predict the severity of the upcoming season in Australia according to Professor Patrick Reading, Director of the WHO Collaborating Centre for Reference and Research on Influenza. […] Despite the increased influenza activity, we cant currently predict the severity of the upcoming season in Australia said Professor Reading. […] The WHO Global Influenza Surveillance and Response System monitors circulating virus strains worldwide and convenes biannual meetings to recommend candidate vaccine viruses for the upcoming flu seasons in each hemisphere. […] Professor Paul Griffin highlighted the severity of influenza compared to other viral respiratory infections and discussed the best preventative and treatment measures. […] Its always a bad flu season because its hospitalising and killing people and making them sickit doesnt necessarily need to be a record flu season for it to be important, said Professor Leask.

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