CDC’s Influenza Vaccine Effectiveness Networks
In the United States, CDC and the Advisory Committee on Immunization Practices (ACIP) recommends annual influenza vaccination for all persons older than 6 months of age. Monitoring the performance of influenza vaccines is important for understanding and improving the benefits of vaccine. CDC uses four primary networks to estimate vaccine effectiveness (VE): the Flu VE Network, the Influenza Vaccine Effectiveness in the Critically Ill (IVY), the National Vaccine Surveillance Network (NVSN), and the VISION VE Network. The Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN) was previously used to estimate VE among hospitalized adults but ended enrollment July 31, 2021. CDC will continue to collect information on adults hospitalized with influenza through its other VE networks.
Some influenza vaccine effectiveness networks are also used to evaluate the effectiveness of other vaccines, including COVID-19 vaccines. Those data can be found online.
Started in 2003-04 and collects vaccine effectiveness data on outpatient illness with laboratory-confirmed flu.
Started in 2019 to collect data on how well flu vaccines work at preventing severe flu among intensive care unit (ICU) patients. As of April 1, 2021, IVY has expanded to also enroll all patients hospitalized with COVID-19. During the 2021-2022 flu season, the network will also enroll patients hospitalized with flu.
Started in 2015-16 and collects vaccine effectiveness data on pediatric hospitalizations with laboratory-confirmed flu in children 18 years of age and younger.
Additional Studies Evaluating Vaccine Effectiveness
Started in 2021 and prospectively collects data on people with laboratory-confirmed influenza or SARS-CoV-2 and assesses rates of transmission to household members. The data are used to compare rates of household transmission from vaccinated versus unvaccinated people.
A research collaboration between CDC, Westat, and multiple sites in the United States to conduct randomized trials to evaluate how well different influenza vaccines protect people 18-64 years old against influenza (flu).
Previous Vaccine Effectiveness Networks
HAIVEN ended enrollment July 31, 2021 and is not being used this season. Started in 2015-16, it collected vaccine effectiveness data on hospitalizations with laboratory-confirmed flu in adults 18 years of age and older.
See Seasonal Influenza Vaccine Effectiveness, 2004-2021 for season-by-season data and references.