Optimal biannual COVID-19 vaccine boosting dates for those aged 65 and over

Background: To mitigate transmission and reduce the morbidity and mortality, the CDC recommends that individuals aged 65 and older receive a second dose of the 2024-2025 COVID-19 vaccine six months after their first booster dose. However, the optimal dates for biannual boosting are unknown. Geographic variation in infection rates throughout the year make it challenging to intuit the best yearly booster administration date to effectively prevent infection. With rapid waning and strong peaks associated with seasonality, precise timing of booster administration can maximize clinical and public health benefits. Methods: We integrated longitudinal antibody waning trajectories, reinfection probabilities, and spatiotemporal projections of COVID-19 incidence to construct a geographically resolved model for optimizing booster timing in adults aged 65 and older. Results: The benefit of dual booster vaccination is substantially increased by optimal timing, conferring as much as a 3-4-fold decrease in infection risk over five years. This benefit depends not only on the date of initial vaccination but also on the date of the second boost, which often falls outside of the current 6 month recommendation. In New York, for instance, optimal biannual booster dates are September 21 and February 22. In general, they are location-specific, relating to the geography of seasonal incidence. Conclusions: Substantial benefit accrues from aptly timing dual COVID-19 booster vaccination campaigns for individuals over 65. Booster vaccination should be tailored to specific locations and anticipate regional periods of peak transmission. Analyses provide location-specific guidance for public health policy, healthcare provider recommendations, and individual decision-making.