Effects of Influenza Vaccination in the United States during the 2017-2018 Influenza Season.
Clin Infect Dis. 2019 Feb 02;:
Authors: Rolfes MA, Flannery B, Chung J, O'Halloran A, Garg S, Belongia EA, Gaglani M, Zimmerman R, Jackson ML, Monto AS, Alden NB, Anderson E, Bennett NM, Billing L, Eckel S, Kirley PD, Lynfield R, Monroe ML, Spencer M, Spina N, Talbot HK, Thomas A, Torres S, Yousey-Hindes K, Singleton J, Patel M, Reed C, Fry AM, U.S. Flu VE Network, the Influenza Hospitalization Surveillance Network (FluSurv-NET), and the Assessment Branch, Immunization Services Division, Centers for Disease Control and Prevention
Background: The severity of the 2017-2018 influenza season in the U.S. was high with influenza A(H3N2) viruses predominating. We report influenza vaccine effectiveness (VE) and estimate the number of vaccine prevented influenza-associated illnesses, medical visits, hospitalizations, and deaths for the 2017-2018 influenza season.
Methods: We used national age-specific estimates of 2017-2018 influenza vaccine coverage and disease burden. We estimated VE, and 95% confidence intervals (CI), against medically-attended RT-PCR confirmed influenza virus infection, in the ambulatory setting, using a test-negative design. We estimated influenza type/subtype-specific burden using multipliers applied to population-based rates of influenza-associated hospitalizations. We used a compartmental model to estimate numbers, with 95% credible intervals (CrI), of influenza-associated outcomes prevented by vaccination.
Results: The VE against outpatient medically-attended, laboratory-confirmed influenza was 38% (95% CI: 31-43%) including 22% (95% CI: 12-31%) against influenza A(H3N2), 62% (95% CI: 50-71%) against influenza A(H1N1)pdm09, and 50% (95% CI: 41-57%) against influenza B. We estimated that influenza vaccination prevented 7.1 million (95% CrI: 5.4 million-9.3 million) illnesses, 3.7 million (95% CrI: 2.8 million-4.9 million) medical visits, 109,000 (95% CrI: 39,000-231,000) hospitalizations, and 8,000 (95% CrI: 1,100-21,000) deaths. Vaccination prevented 10% of expected hospitalizations overall and 41% among young children (6 months-4 years).
Conclusions: Despite 38% VE, influenza vaccination reduced a substantial burden of influenza-associated illness, medical visits, hospitalizations, and deaths in the U.S. during the 2017-2018 season. Our results demonstrate the benefit of current influenza vaccination and the need for improved vaccines.
PMID: 30715278 [PubMed - as supplied by publisher]