CDC's Influenza Vaccine Effectiveness Networks

What to know

In the United States, seasonal influenza (flu) vaccines become available every year for use in people 6 months and older. Monitoring how well flu vaccines work, or vaccine effectiveness (VE), is important for understanding the impact of flu vaccination.

A person wearing a lab coat, safety goggles, a face mask, and blue latex gloves.

Overview

CDC conducts flu VE studies using multiple networks, listed below. These networks evaluate flu vaccine effectiveness across various populations and outcomes.

US FLU VE NETWORK

Started in 2004-2005 and collects vaccine effectiveness data on outpatient illness with laboratory-confirmed flu.

NVSN

Started in 2015-2016 and collects vaccine effectiveness data on pediatric hospitalizations with laboratory-confirmed flu in children younger than 18 years.

VISION

Started in 2019 and collects data to evaluate how well vaccines and preventive products (e.g., monoclonal antibodies) work to protect people from illness and complications caused by infection with seasonal influenza (flu) viruses, respiratory syncytial virus (RSV), and SARS-CoV-2 (COVID-19).

Previous flu vaccine effectiveness networks

IVY

IVY ended enrollment in 2025. IVY collected data on how well flu vaccines worked at preventing severe flu among adults hospitalized with flu.

Respiratory Virus Transmission Network

RVTN ended enrollment in 2025. RVTN prospectively collected data on people with laboratory-confirmed flu or COVID-19 and assessed rates of transmission to household members. The data were used to compare household transmission among vaccinated people to household transmission among unvaccinated people.

Randomized Assessment of Influenza Vaccine Efficacy Network (RAIVEN)

RAIVEN ended enrollment in 2022. RAIVEN was a research collaboration between CDC, Westat, and multiple sites in the United States that conducted randomized trials to evaluate how well different flu vaccines protect people 18-64 years against flu.

HAIVEN

HAIVEN ended enrollment in 2021. HAIVEN collected vaccine effectiveness data on hospitalizations with laboratory-confirmed flu in adults 18 years and older.
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Content Source:
National Center for Immunization and Respiratory Diseases (NCIRD)