CDC’s Influenza Vaccine Effectiveness Networks
In the United States, CDC and the Advisory Committee on Immunization Practices (ACIP) recommend annual influenza (flu) vaccination for all people 6 months and older. Monitoring the performance of flu vaccines is important for understanding and improving the benefits of flu vaccination. Over the past few years, CDC has conducted VE studies using multiple networks, including the U.S. Flu VE Network, Influenza and Other Viruses in the Acutely Ill (IVY) Network, 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 it ended enrollment on July 31, 2021, and is no longer being used. CDC continues to collect information on adults hospitalized with flu through IVY and VISION. Additional studies evaluating VE include the Respiratory Virus Transmission Network (RVTN) and the Randomized Assessment of Influenza Vaccine Efficacy Network (RAIVEN).
Some flu 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 2003-2004 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. In 2021, IVY expanded to also enroll all patients hospitalized with flu or COVID-19, and in 2022, IVY expanded again to enroll patients hospitalized with respiratory syncytial virus (RSV).
Started in 2015-2016 and collects vaccine effectiveness data on pediatric hospitalizations with laboratory-confirmed flu in children 18 years and younger.
Started in 2019 and collects data to evaluate how well seasonal flu vaccines protect people against flu and how well different COVID-19 vaccines protect against COVID-19.
Additional Studies Evaluating Vaccine Effectiveness
Started in 2021 and prospectively collects data on people with laboratory-confirmed flu or COVID-19 and assesses rates of transmission to household members. The data are used to compare household transmission among vaccinated people to household transmission among unvaccinated people.
A research collaboration between CDC, Westat, and multiple sites in the United States to conduct randomized trials to evaluate how well different flu vaccines protect people 18-64 years old against flu.
Previous Vaccine Effectiveness Networks
HAIVEN ended enrollment July 31, 2021, and is no longer being used. Started in 2015-2016, it collected vaccine effectiveness data on hospitalizations with laboratory-confirmed flu in adults 18 years and older.
Season-by-season data and references for each season starting in 2004-2005 are available at Seasonal Influenza Vaccine Effectiveness.