Influenza vaccine effectiveness against hospitalizations and emergency department or urgent care encounters for children, adolescents, and adults during the 2023-2024 season, United States.

Tenforde MW, Reeves EL, Weber ZA, Tartof SY, Klein NP, Dascomb K, DeSilva MB, Yang DH, Grannis SJ, Irving SA, Ong TC, Link-Gelles R, Salas SB, Sy LS, Lewin B, Contreras R, Zerbo O, Fireman B, Hansen J, Timbol J, Sheffield T, Bride D, Arndorfer J, VanOtterloo J, McEvoy CE, Akinsete OO, Essien IJ, Dixon BE, Rogerson C, Fadel WF, Duszynski T, Naleway AL, Barron MA, Rao S, Mayer D, Chavez C, Ball SW, Payne AB, Ray C, Dickerson M, Neelam V, Adams K, Flannery B, DeCuir J, Garg S. Influenza vaccine effectiveness against hospitalizations and emergency department or urgent care encounters for children, adolescents, and adults during the 2023-2024 season, United States. Clinical infectious diseases : an official publication of the Infectious Diseases Society of America. 2024 Dec 4.

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Abstract:

BACKGROUND: The 2023-2024 influenza season had predominant influenza A(H1N1)pdm09 virus activity, but A(H3N2) and B viruses co-circulated. Seasonal influenza vaccine strains were well-matched to these viruses. METHODS: Using health care encounters data from health systems in 8 states, we evaluated influenza vaccine effectiveness (VE) against influenza-associated medical encounters from October 2023-April 2024. Using a test-negative design, we compared the odds of vaccination between patients with an acute respiratory illness (ARI) who tested positive (cases) versus negative (controls) for influenza by molecular assay, adjusting for confounders. VE was stratified by age group, influenza type (overall, influenza A, influenza B), and care setting (hospitalization, emergency department or urgent care [ED/UC] encounter). RESULTS: Overall, 74,000 encounters in children and adolescents aged 6 months - 17 years (3,479 hospitalizations, 70,521 ED/UC encounters) and 267,606 in adults aged 18 years (66,828 hospitalizations, 200,778 ED/UC encounters) were included. Across care settings, among children and adolescents 15% (2,758/17,833) of cases versus 32% (18,240/56,167) of controls had received vaccination. Among adults, 25% (11,632/46,614) of cases versus 44% (97,811/220,992) of controls across care settings had received vaccination. VE was 58% (95% confidence interval [95% CI]: 44-69%) against hospitalization and 58% (95% CI: 56-60%) against ED/UC encounters for children and adolescents, and 39% (95% CI: 35-43) against hospitalization and 47% (95% CI: 46-49%) against ED/UC encounters for adults. Across age groups, VE was higher against influenza B than influenza A. CONCLUSIONS: Influenza vaccines provided protection against influenza-associated illness across health care settings and age groups during the 2023-2024 influenza season.