Influenza vaccination showed benefits in reducing infections to both vaccinated and unvaccinated individuals, even when both effectiveness and uptake were low, according to results of an analytical model study published in JAMA Network Open. However, they noted when transmission was high, even highly effective vaccines did not protect those who were unvaccinated.1
Even when transmission was high, highly effective vaccines did not protect those who were unvaccinated. | Image Credit: Aron M – Austria – stock.adobe.com
“In our results, a substantial proportion of infections was prevented when transmissibility was similar to that encountered in typical influenza seasons, vaccine effectiveness was within the ranges estimated for those seasons, and vaccine uptake was similar to what is typically found in the US,” the study authors said.1
Flu vaccination can help prevent illness, and according to the CDC, in the 2019 to 2020 flu season, vaccination prevented approximately 7 million influenza illnesses, 3 million influenza-associated medical visits, 100,000 influenza-associated hospitalizations, and 7000 influenza-associated deaths in the US. Because every flu season is different, getting vaccinated each season is essential. The CDC recommends that patients 6 months and older should get a flu vaccine every season, especially for patients who are at higher risk of serious complications due to illness.2
Investigators of the current study modeled influenza infection following populations of both vaccinated and unvaccinated individuals. The infection was modeled to include different levels of transmission, effectiveness, and uptake to estimate direct and indirect benefits of vaccination as well as disease burden. Vaccination uptake of approximately 51%, except for scenarios where vaccination rates were studied. Overall vaccination uptake rates ranged from 22% to 71% in these simulations.1
The population included 1,218,695 hypothetical patients, with 51% being female and a median age of 40.6 years. The mean reduction of cases ranged from 41.5% to 70.3% in low transmission scenarios, from 34.3% to 56.6% in moderate transmission scenarios, and from 32.9% to 48.1% in high transmission scenarios. The overall reduction in burden was modest when only a small number of patients were vaccinated and when vaccine effectiveness was low, even for high transmission cases. When effectiveness was around 60%, cases were almost eliminated when approximately 56% of the population was vaccinated in the lowest transmission scenarios.1
As for the benefits of vaccination, case burden decreased with vaccination for both vaccinated and unvaccinated individuals. However, in these scenarios, the benefits were higher for vaccinated individuals.1
“Although substantial, the indirect benefit to the unvaccinated population was always less than the direct benefit to the vaccinated population. Indirect benefit in our results was greatest when both virus transmissibility and vaccine effectiveness were low,” the study authors said.1 “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.”
Pharmacists have the potential to significantly improve vaccine coverage among older adults, who are often at high risk for severe disease. The role of the pharmacist has been growing significantly, with pharmacies administering over 270 million COVID-19 vaccines and another 8.1 million in long-term care residencies from February 2020 through September 2022.3
READ MORE: Influenza Resource Center
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