Abstract
This analysis assessed differences in influenza vaccine effectiveness (VE) and severe in-hospital outcomes between U.S. male and female adults hospitalized with laboratory-confirmed influenza in a multi-center network during 2022–2024. Compared with men, women hospitalized with influenza were less likely to smoke (21.5 % vs 25.3 %, P = 0.02), to have COPD (21.9 % vs 22.7 %, P < 0.001), and to be admitted to an intensive care unit once hospitalized (17.3 % vs 20.7 %, P = 0.04). Influenza VE (95 % confidence interval [CI]) was significantly higher in women aged ≥50 years compared with men aged ≥50 years (48.5 % [39.2 %–56.4 %] vs 26.2 % [13.0 %–37.5 %]). VE was slightly lower in women aged 18–49 years compared with women ≥50 years (46.2 % [95 % CI: 24.2 %–61.8 % vs 61.3 % [41.0 %–74.6 %]) but significantly lower in men aged ≥50 years compared with men aged 18–49 years (61.3 % [41.0 %–74.6 %] vs 26.2 % [13.0 %–37.5 %]). Disaggregation of sex should be considered in future influenza VE studies.