Background: Annual vaccination against seasonal influenza is recommended for all persons ages ≥6 months in the U.S., as it is effective in reducing influenza-related illness and death. However, data show that only 44% of U.S. adults were vaccinated in the 2024-25 season. Previous research indicates that low vaccination uptake is linked to sociodemographic characteristics, region and health insurance status. We assessed trends in influenza vaccination coverage between 2017-18 and 2022-23 seasons and evaluated factors associated with uptake in U.S. Military Health System (MHS) beneficiaries during the 2022-2023 influenza season.

Methods: We performed a cross-sectional study using all eligible beneficiaries ages 1-64 years between July 2017 and March 2023. We used chi-square tests to compare vaccination rates between the first and last season and multivariable logistic regression to assess factors associated with vaccination coverage in the 2022-23 season.

Results: We identified 6,006,857 eligible MHS beneficiaries over the six influenza seasons. Vaccination rates between the first and last influenza season increased from 33% to 36.5% (p-value < 0.0001). We observed significant decreases in vaccination rates over the study period among ages 5-17, dependent beneficiaries, and those in the Northeastern U.S. In 2022-23, female beneficiaries were more likely to be vaccinated than males (aOR 1.33, p-value < 0.0001). In addition, Black, Hispanic, and Asian/Pacific Islander beneficiaries had marginally higher rates of coverage as compared to White beneficiaries (aOR: 1.07, 1.10, 1.18, p-value < 0.0001).

Conclusions: Our results indicate that overall influenza vaccination rates increased between 2017 and 2023, however, use of the EHR systems alone for tracking vaccination data tends to underestimate coverage in the MHS. Tailored strategies are needed to improve influenza vaccination uptake to prevent illness, hospitalization and death.