Influenza vaccine effectiveness among outpatients in the US Influenza Vaccine Effectiveness Network by study site 2011‐2016

• Published in: Influenza and other respiratory viruses Vol. 14; no. 4; pp. 380 - 390
• Main Authors: Balasubramani, Goundappa K., Nowalk, Mary Patricia, Sax, Theresa M., Suyama, Joe, Bobyock, Emily, Rinaldo, Charles R., Martin, Emily T., Monto, Arnold S., Jackson, Michael L., Gaglani, Manjusha J., Flannery, Brendan, Chung, Jessie R., Zimmerman, Richard K.
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01-07-2020; John Wiley and Sons Inc
• Subjects: Age; Analysis; Clinics; Cough; Demographics; Disease control; Enrollments; Estimates; Ethnicity; Health maintenance organizations; Hispanic Americans; HMOs; Illnesses; Immunization; Infections; Influenza; influenza vaccine; Influenza vaccines; Medical laboratories; Medical records; Medical research; Medicine, Experimental; Minority & ethnic groups; Original; Pharmacy; Polymerase chain reaction; Population; Regression analysis; Regression models; Respiratory diseases; Seasons; Statistical analysis; Studies; Vaccination; vaccine effectiveness; Vaccine efficacy; Vaccines; Variables; Viruses; United States > US; Michigan; influenza; vaccine effectiveness; influenza vaccine
• ISSN: 1750-2640; 1750-2659
• DOI: 10.1111/irv.12741

Background
Influenza vaccination is recommended for all US residents aged ≥6 months. Vaccine effectiveness (VE) varies by age, circulating influenza strains, and the presence of high‐risk medical conditions. We examined site‐specific VE in the US Influenza VE Network, which evaluates annual influenza VE at ambulatory clinics in geographically diverse sites.
Methods
Analyses were conducted on 27 180 outpatients ≥6 months old presenting with an acute respiratory infection (ARI) with cough of ≤7‐day duration during the 2011‐2016 influenza seasons. A test‐negative design was used with vaccination status defined as receipt of ≥1 dose of any influenza vaccine according to medical records, registries, and/or self‐report. Influenza infection was determined by reverse‐transcription polymerase chain reaction. VE estimates were calculated using odds ratios from multivariable logistic regression models adjusted for age, sex, race/ethnicity, time from illness onset to enrollment, high‐risk conditions, calendar time, and vaccination status‐site interaction.
Results
For all sites combined, VE was statistically significant every season against all influenza and against the predominant circulating strains (VE = 19%‐50%) Few differences among four sites in the US Flu VE Network were evident in five seasons. However, in 2015‐16, overall VE in one site was 24% (95% CI = −4%‐44%), while VE in two other sites was significantly higher (61%, 95% CI = 49%‐71%; P = .002, and 53%, 95% CI = 33,67; P = .034).
Conclusion
With few exceptions, site‐specific VE estimates aligned with each other and overall VE estimates. Observed VE may reflect inherent differences in community characteristics of the sites and highlights the importance of diverse settings for studying influenza vaccine effectiveness.