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Influenza vaccine effectiveness against influenza-associated hospitalizations and emergency department or urgent care encounters among children and adults - United States, 2024-25 season

DeCuir, J.; Reeves, E. L.; Weber, Z. A.; Yang, D.-H.; Irving, S. A.; Tartof, S. Y.; Klein, N. P.; Grannis, S. J.; Ong, T. C.; Ball, S. W.; DeSilva, M. B.; Dascomb, K.; Naleway, A. L.; Koppolu, P.; Salas, S. B.; Sy, L. S.; Lewin, B.; Contreras, R.; Zerbo, O.; Hansen, J. R.; Block, L.; Jacobson, K. B.; Dixon, B. E.; Rogerson, C.; Duszynski, T.; Fadel, W. F.; Barron, M. A.; Mayer, D.; Chavez, C.; Yates, A.; Kirshner, L.; McEvoy, C. E.; Akinsete, O. O.; Essien, I. J.; Sheffield, T.; Bride, D.; Arndorfer, J.; Van Otterloo, J.; Natarajan, K.; Ray, C. S.; Payne, A. B.; Adams, K.; Flannery, B.; Garg,

2026-04-24 public and global health
10.64898/2026.04.22.26350853 medRxiv
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BackgroundThe 2024-25 influenza season was the most severe in the United States (US) since 2017-18, with co-circulation of both influenza A virus subtypes (H1N1 and H3N2). Influenza vaccine effectiveness (VE) has varied by season, setting, and patient characteristics. MethodsUsing electronic healthcare encounter data from eight US states, we evaluated influenza vaccine effectiveness (VE) against influenza-associated hospitalizations and emergency department or urgent care (ED/UC) encounters from October 2024-April 2025 among children aged 6 months-17 years and adults aged [≥]18 years. Using a test-negative, case-control design, we compared the odds of influenza vaccination between acute respiratory illness (ARI) encounters with a positive (cases) versus negative (controls) test for influenza by molecular assay, adjusting for confounders. ResultsAnalyses included 108,618 encounters (5,764 hospitalizations and 102,854 ED/UC encounters) among children and 309,483 encounters (76,072 hospitalizations and 233,411 ED/UC encounters) among adults. Among children across care settings, 17.0% (6,097/35,765) of cases versus 29.4% (21,449/72,853) of controls were vaccinated. Among adults, 28.2% (21,832/77,477) of cases versus 44.2% (102,560/232,006) of controls were vaccinated. VE was 51% (95% confidence interval [95% CI]: 41-60%) against influenza-associated hospitalizations and 54% (95% CI: 52-55%) against influenza-associated ED/UC encounters among children. VE was 43% (95% CI: 41-46%) against influenza-associated hospitalizations and 49% (95% CI: 47-50%) against influenza-associated ED/UC encounters among adults. ConclusionsInfluenza vaccination provided protection against influenza-associated hospitalizations and ED/UC encounters among children and adults in the US during the severe 2024-25 influenza season. These findings support influenza vaccination as an important tool to reduce influenza-associated disease. Brief SummaryDuring the 2024-25 influenza season, influenza vaccination provided protection against influenza-associated hospitalizations (43-51%) and emergency department or urgent care encounters (49-54%) among children and adults in the United States.

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