Influenza Vaccine Effectiveness Against Influenza A–Associated Emergency Department, Urgent Care, and Hospitalization Encounters Among US Adults, 2022–2023
Mark W. Tenforde, Zachary A. Weber, Duck‐Hye Yang, Malini B. DeSilva, Kristin Dascomb, Stephanie A. Irving, Allison L. Naleway, Manjusha Gaglani, Bruce Fireman, Ned Lewis, Ousseny Zerbo, Kristin Goddard, Julius Timbol, John Hansen, Nancy Grisel, Julie Arndorfer, Charlene McEvoy, Inih Essien, Suchitra Rao, Shaun J. Grannis, Anupam B. Kharbanda, Karthik Natarajan, Toan C. Ong, Peter J. Embí, Sarah W. Ball, Margaret M. Dunne, Lindsey Kirshner, Ryan E. Wiegand, Monica Dickerson, Palak Patel, Caitlin Ray, Brendan Flannery, Shikha Garg, Katherine Adams, Nicola P. Klein
Abstract
BACKGROUND: The 2022-2023 United States influenza season had unusually early influenza activity with high hospitalization rates. Vaccine-matched A(H3N2) viruses predominated, with lower levels of A(H1N1)pdm09 activity also observed. METHODS: Using the test-negative design, we evaluated influenza vaccine effectiveness (VE) during the 2022-2023 season against influenza-A-associated emergency department/urgent care (ED/UC) visits and hospitalizations from October 2022-March 2023 among adults (age ≥18 years) with acute respiratory illness (ARI). VE was estimated by comparing odds of seasonal influenza vaccination among case-patients (influenza A test-positive by molecular assay) and controls (influenza test-negative), applying inverse-propensity-to-be-vaccinated weights. RESULTS: The analysis included 85,389 ED/UC ARI encounters (17.0% influenza-A-positive; 37.8% vaccinated overall) and 19,751 hospitalizations (9.5% influenza-A-positive; 52.8% vaccinated overall). VE against influenza-A-associated ED/UC encounters was 44% (95% confidence interval [95%CI]: 40-47%) overall and 45% and 41% among adults aged 18-64 and ≥65 years, respectively. VE against influenza-A-associated hospitalizations was 35% (95%CI: 27-43%) overall and 23% and 41% among adults aged 18-64 and ≥65 years, respectively. CONCLUSIONS: VE was moderate during the 2022-2023 influenza season, a season characterized with increased burden of influenza and co-circulation with other respiratory viruses. Vaccination is likely to substantially reduce morbidity, mortality, and strain on healthcare resources.