Speaker
Description
During the COVID-19 pandemic early years, infection-prevention measures suppressed influenza transmission and the early onset and moderate severity of the US 2022-2023 influenza season may have resulted from lower population immunity after two years of limited influenza virus circulation. We used an age stratified mathematical model of influenza virus transmission that incorporates vaccine-derived protection against both infection and severe disease to estimate the impact of influenza vaccines on healthcare burden. Assuming reported levels of past vaccine effectiveness (VE) against infection and hospitalization, we estimate that influenza vaccines prevented 69,886 [95% CI: 51,860 – 84,575] influenza-related hospitalizations nationwide during the 2022-2023 season, with 57% attributable to reduced susceptibility and onward transmission. Despite limited data on VE against infection, our analyses suggest substantial indirect protection, particularly from young adults to other age groups. This is supported by a significant negative correlation between young adult (aged 18-49 years) vaccination rates and observed hospital burden across US states. Among those aged >=65 years, nearly half of averted hospitalizations resulted from vaccinating younger age groups. These findings highlight the need for better estimates of influenza VE against infection and the potential benefits of increasing young adult influenza vaccination rates to reduce both direct and indirect disease burden.
Bibliography
@article{Bi2025InfluenzaVaccineImpact,
author = {Bi, K. and others},
title = {Estimated impact of 2022--2023 influenza vaccines on annual hospital burden in the United States},
journal = {Proceedings of the National Academy of Sciences},
year = {2025},
volume = {122},
number = {},
pages = {},
doi = {10.1073/pnas.2505175122},
publisher = {National Academy of Sciences}
}
