A new study published in JAMA Network Open has found that vaccinated individuals can indirectly benefit from living in a highly vaccinated population, reducing their risk of acquiring the flu virus. Researchers used an agent-based model to estimate the impact of influenza vaccination on both directly vaccinated and unvaccinated populations.
Influenza seasons vary widely, with U.S. symptomatic cases estimated at 9 million to over 40 million between 2010 and 2024. Vaccination is the safest and most effective way to prevent the disease, but not everyone can or will be vaccinated in a given population.
The study simulated a digital cohort of 1,218,695 individuals with demographic attributes, household locations, and simulated schools and workplaces. Agents were vaccinated at an age-specific uptake rate that yielded 51% overall. The researchers varied vaccine effectiveness from 40% to 60% and tested scenarios ranging from modest transmission to extreme levels above 5.0.
Results showed that vaccination prevented 32.9% to 41.5% of infections in the simulated population, extending protection even to some unvaccinated residents. Direct benefits to vaccinated agents exceeded indirect benefits in every seasonal scenario. However, when transmission climbed to pandemic levels, only vaccinated individuals remained shielded from infection.
The study concludes that influenza vaccination delivers substantial community protection during typical seasons, with indirect benefits appearing when transmission is low and vaccine effectiveness is high. This finding highlights the importance of herd immunity for those who cannot be vaccinated, such as infants under 6 months or those with specific medical conditions or vaccine allergies.
Source: https://medicalxpress.com/news/2025-07-vaccinated-people-benefit-flu-shot.html