Improving flu vaccination rates in young adults may significantly reduce hospitalizations, according to a new study

Researchers find that improving flu vaccination rates in young adults may significantly reduce hospitalizations, according to a new study published in Proceedings of the National Academy of Sciences.  

The publication, led by Kaiming Bi, PhD, assistant professor in the Department of Management, Policy, and Community Health at UTHealth Houston School of Public Health, found that flu vaccines prevented roughly 70,000 hospitalizations during the 2022-2023 season, and that an additional 19,000 hospital stays could have been avoided had there been higher vaccination coverage. 

Flu vaccination rates in the U.S. have slowly trended upward over the last decade, rising from 41.8% in 2011–2012 to 49.3% in 2022–2023. However, the rates still fall short of the federal Healthy People target of 70% coverage by the year 2030. The Healthy People 2030 initiative includes over 350 objectives to improve the nation's health, including improving health behaviors, reducing chronic diseases, and expanding public health infrastructure. 

Increasing vaccination coverage can strengthen population immunity and offer indirect protection to those at higher risk of severe illness, including young children, older adults, and people who are immunocompromised. 

To estimate the impact of increased flu vaccinations, Bi and his team used a mathematical model in which three virus transmission scenarios considered vaccine effectiveness in directly reducing the severity and susceptibility to the flu.  

Researchers’ analysis found that flu shots prevented 69,886 hospitalizations during the 2022-2023 season, with 57% of that attributed to decreased susceptibility and reduced transmission in communities.  

The study also identified a strong link between higher vaccination rates among adults ages 18 to 49 and lower hospitalization rates across the nation. While the 18 to 49 age group had the lowest vaccination rate, their flu vaccination indirectly reduced hospitalizations among adults 65 and older by 4.8%, preventing 12.5 hospitalizations per 100,000 people.  
Among ages 65 and older, nearly half of the hospitalizations avoided were linked to vaccinations in younger age groups, highlighting the significance of indirect protection. 

“Our analyses suggest that, without influenza vaccines, there would have been roughly 24% more influenza hospitalizations during the 2022 to 2023 influenza season,” said Bi.  

These models let us look at the impact of previous flu vaccination campaigns and understand how raising vaccination rates in specific age groups could help prevent more illness. “Mathematical modeling helps quantify the population-level impact of vaccination, including how many hospitalizations are prevented,” shared Bi. “It also allows us to evaluate “what-if” scenarios—such as changes in vaccine uptake or vaccine effectiveness—which can guide public health decision-making and intervention planning.” 

Insight from Bi’s model reinforces the importance of improving vaccination rates, particularly among young adults, whose immunization can substantially benefit the broader population. 

Additional authors include Shraddha Ramdas Bandekar, PhD; Anass Bouchnita, PhD; Annalise Cramer; Spencer J. Fox, PhD; Rebecca K. Borchering, PhD; Matthew Biggerstaff, ScD, MPH; and Lauren Ancel Meyers, PhD.