Influenza Vaccine Effectiveness Against Hospitalization in the United States, 2019–2020
Mark W. Tenforde, H. Keipp Talbot, Christopher Trabue, Manjusha Gaglani, Tresa McNeal, Arnold S. Monto, Emily T. Martin, Richard K. Zimmerman, Fernanda P. Silveira, Donald B. Middleton, Samantha M. Olson, Rebecca Kondor, John Barnes, Jill M. Ferdinands, Manish M. Patel, Shoshona Le, Juliana da Silva, Lisa M. Keong, Thomas Stark, Joshua G. Petrie, Lois Lamerato, Anurag N. Malani, Adam S. Lauring, Ryan E. Malosh, Dayna Wyatt, Yuwei Zhu, Zhouwen Liu, Stephanie Longmire, Kellie Graves, Emily Sedillo, Alina Simion, Karen Speer, Bethany Alicie, Briana Krantz, Donna Carillo, Laura E. Adams, A. M. Drennan, Jan Orga, Lynn M. Peterson, Natasha Halasa, Rendi McHenry, Claudia Guevara Pulido, Kempapura Murthy, Kelsey Bounds, Tnelda Zunie, Lydia Clipper, Shekhar Ghamande, Heath D. White, Chandni Raiyani, Kevin Chang, Arundhati Rao, Manohar B. Mutnal, Alejandro C. Arroliga, Mary Patricia Nowalk, K G Balasubramani, Heather Eng, Sean Saul, Kailey Hughes, Nicole Wheeler, Lori Stiefel, Mohamed Yassin, John V. Williams
Abstract
BACKGROUND: Influenza causes significant morbidity and mortality and stresses hospital resources during periods of increased circulation. We evaluated the effectiveness of the 2019-2020 influenza vaccine against influenza-associated hospitalization in the United States. METHODS: We included adults hospitalized with acute respiratory illness at 14 hospitals and tested for influenza viruses by reserve-transcription polymerase chain reaction. Vaccine effectiveness (VE) was estimated by comparing the odds of current-season influenza vaccination in test-positive influenza cases vs test-negative controls, adjusting for confounders. VE was stratified by age and major circulating influenza types along with A(H1N1)pdm09 genetic subgroups. RESULTS: A total of 3116 participants were included, including 18% (n = 553) influenza-positive cases. Median age was 63 years. Sixty-seven percent (n = 2079) received vaccination. Overall adjusted VE against influenza viruses was 41% (95% confidence interval [CI], 27%-52%). VE against A(H1N1)pdm09 viruses was 40% (95% CI, 24%-53%) and 33% against B viruses (95% CI, 0-56%). Of the 2 major A(H1N1)pdm09 subgroups (representing 90% of sequenced H1N1 viruses), VE against one group (5A + 187A,189E) was 59% (95% CI, 34%-75%) whereas no VE was observed against the other group (5A + 156K) (-1% [95% CI, -61% to 37%]). CONCLUSIONS: In a primarily older population, influenza vaccination was associated with a 41% reduction in risk of hospitalized influenza illness.