Frequent COVID-19 Booster Vaccination Reduces Severe Disease Risk Across Key Groups

Frequent COVID-19 booster vaccinations significantly lower the risk of severe disease, particularly in older adults and immunocompromised individuals, according to a study published in Nature Communications.

“Using a microsimulation model, which is a common public health modeling approach that allows the simulation of individual people with unique characteristics, we model SARS-CoV-2 infection and severe COVID-19 to compare the impact of various timings of COVID-19 booster vaccination in different risk groups,” explained Hailey Park, Division of Infectious Diseases and Geographic Medicine, Department of Medicine, Stanford University, Stanford, CA, and coauthors.

The research, based on US COVID-19 surveillance data and vaccination records, modeled the effectiveness of various booster schedules over a 2-year period, providing critical insights for vaccine policy. The researchers aimed to inform guidance for the frequency of booster vaccination in the US.

Annual and semiannual booster vaccinations substantially reduced the risk of severe COVID-19—defined as hospitalization or death—compared with a one-time booster dose. In adults aged 75 years and older, annual boosters reduced severe cases by 199 per 100 000 people annually, whereas semiannual boosters achieved a reduction of 368 cases per 100 000. In immunocompromised individuals, the benefits were similarly pronounced, with reductions of 184 and 310 cases per 100 000 for annual and semiannual boosters, respectively.

The analysis also highlighted the diminishing protection provided by prior vaccination and natural infection due to waning immunity and the emergence of new variants. Frequent boosters counteracted this decline effectively, particularly in high-risk populations. For younger adults (18-49 years), the reductions were smaller but still meaningful, with semiannual boosters reducing severe cases by 26 per 100 000.

Scenarios involving novel variants demonstrated that variant-specific booster vaccines could amplify the benefits of frequent boosting, particularly in older adults. Under a scenario with annual novel variant circulation, semiannual boosters reduced severe cases in individuals aged 65-74 years by 134 per 100 000.

The study also explored the indirect effects of booster vaccination through reduced transmission. A dynamic transmission model revealed that frequent boosters in broader populations could further protect high-risk groups, such as those aged 75 years and older.

“In this study, we find that guidance on frequency of COVID-19 booster vaccination may be strengthened by considering risk of severe COVID-19 defined by age and immunocompromised status to mitigate the burden of COVID-19 in the United States,” concluded the study authors. “These results may support guidance decisions on booster timing.”

Reference

Park HJ, Gonsalves GS, Tan ST, et al. Comparing frequency of booster vaccination to prevent severe COVID-19 by risk group in the United States. Nat Commun. 2024;15(1):1883. doi:10.1038/s41467-024-45549-9