Flu Shots Cut Infections, Even at Low Use

Study Shows Widespread Protection Despite Varied Effectiveness

Influenza vaccination offers a significant public health benefit by reducing infections for both those vaccinated and unvaccinated, even when vaccine effectiveness and uptake are modest. However, during periods of high transmission, highly effective vaccines alone cannot fully shield individuals who remain unvaccinated.

Vaccination’s Broad Impact

New research published in JAMA Network Open utilized an analytical model to demonstrate these protective effects. The study authors noted that their findings align with typical influenza seasons, where a considerable portion of infections were prevented when transmission levels, vaccine effectiveness, and uptake rates mirrored those commonly observed in the United States.

The Centers for Disease Control and Prevention (CDC) estimates that during the 2019-2020 flu season, vaccinations prevented approximately 7 million illnesses and 3 million medical visits. Vaccinations also averted 100,000 hospitalizations and 7,000 deaths in the U.S. The agency strongly recommends annual flu shots for everyone aged 6 months and older, particularly those at higher risk of severe complications.

Modeling Disease Prevention

The analytical model simulated influenza infections across populations of vaccinated and unvaccinated individuals, exploring various transmission, effectiveness, and uptake scenarios. The simulations assumed a base vaccination uptake of around 51%, with tested rates ranging from 22% to 71%.

The study involved a hypothetical population of over 1.2 million individuals, with 51% female and a median age of 40.6 years. Reductions in cases varied by transmission intensity: 41.5% to 70.3% in low transmission settings, 34.3% to 56.6% in moderate settings, and 32.9% to 48.1% in high transmission scenarios.

Even when vaccine effectiveness reached approximately 60%, cases were nearly eliminated in low transmission scenarios if about 56% of the population was vaccinated. However, a modest reduction in disease burden was observed when vaccination rates were low or vaccine effectiveness was poor, particularly during periods of high transmission.

Direct vs. Indirect Benefits

The research indicated that while vaccination benefited both vaccinated and unvaccinated individuals, the direct benefits to the vaccinated group were consistently greater. The indirect protection offered to the unvaccinated population was most pronounced when both virus transmissibility and vaccine effectiveness were low.

“When transmissibility levels were much higher, as might be expected in a pandemic situation or with a more transmissible pathogen, indirect benefits to the unvaccinated population decreased, and at the highest levels, the indirect benefit was no longer seen.”

—Study Authors

Pharmacists play a crucial role in increasing vaccination rates. In the United States, pharmacies administered over 270 million COVID-19 vaccines between February 2020 and September 2022, highlighting their expanding capacity in public health initiatives. As of the 2023-2024 season, flu vaccine effectiveness ranged from 30% to 60% against circulating strains according to the CDC, underscoring the importance of continued vaccination efforts.