What to know
The U.S. Flu Vaccine Effectiveness (VE) network is designed to provide estimates of clinical effectiveness of licensed flu vaccines by age group and by influenza virus type and subtype.
Overview
The network consists of seven study sites and one coordinating center (Duke University) spread across the United States:
- Arizona State University (Arizona);
- University of Michigan (Michigan);
- Washington University in St. Louis (Missouri);
- University Hospitals of Cleveland (Ohio);
- University of Pittsburgh (Pennsylvania);
- Baylor Scott & White Health (Texas);
- Kaiser Permanente Washington (Washington).
About the Network
Enrollment in the annual study to measure VE begins after laboratory-confirmed influenza (flu) cases are reported in local surveillance for two consecutive weeks and continues for the rest of flu season.
The study uses a test-negative design which compares vaccination rates among persons with confirmed flu illness versus persons with similar illness who do not have flu based on laboratory tests. More information on the study methods used by the U.S. Flu VE Network is available at Study Design Factors.
Vaccination status is defined as receipt of at least one dose of the current season's flu vaccine according to medical records, immunization registries, and/or self-report.
Patients are eligible if they are older than 6 months of age (and therefore eligible to receive flu vaccination) and have reported acute respiratory illness with new or worsening cough within the last 7 days.
Eligible patients complete an enrollment interview and answer basic questions regarding their flu vaccination status, age, underlying health conditions, and other characteristics. Flu vaccination status is later confirmed by reviewing records and immunization databases.
Following enrollment, a respiratory specimen is collected and tested for influenza virus using specific laboratory tests based on reverse transcription polymerase chain reaction (RT-PCR). Influenza viruses are then tested for influenza virus type A or B and subtype (i.e., H1N1 or H3N2).
Vaccine effectiveness estimates are typically adjusted for study site, age, sex, self-rated general health status, race, Hispanic ethnicity, interval from onset to enrollment, and calendar time of illness.