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Estimated #impact of 2022–2023 #influenza #vaccines on annual #hospital #burden in the #USA

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By G.M.

 


Significance

Annual influenza epidemics in the United States cause hundreds of thousands of hospitalizations. Quantifying vaccine impact is vital, yet many analyses overlook vaccines’ dual benefits: directly protecting recipients and indirectly protecting their contacts. Using a mathematical model that accounts for both effects, we estimate that vaccination prevented about 70,000 hospitalizations during the 2022–2023 season, with another 19,000 potentially avoidable if coverage met the 70% national target. Despite uncertainty in vaccine effectiveness against infection, our findings suggest that vaccinating younger adults offers substantial indirect protection for older adults. Tailoring annual vaccination campaigns by age group and state could further strengthen their public health impact.


Abstract

During the COVID-19 pandemic early years, infection prevention measures suppressed transmission of seasonal influenza and other respiratory viruses. The early onset and moderate severity of the US 2022–2023 influenza season may have resulted from reduced use of nonpharmaceutical interventions or lower population immunity after 2 y of limited influenza virus circulation. We used a 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 to 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 to 49 y) vaccination rates and observed hospital burden across US states. Among those aged ≧65 y, 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.

Source: Proceedings of the National Academy of Sciences of the United States of America, https://www.pnas.org/doi/abs/10.1073/pnas.2505175122?af=R

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