Impact of Prioritizing Elderly and High-risk Individuals During COVID-19 Vaccine Allocation

Background: The prioritization of vaccine eligibility for different subpopulations is an important decision to curb spread and severe outcomes of epidemic infectious diseases for which vaccines become available. Using COVID-19 as a prototype, this study evaluates the public health impact of various vaccine prioritization schemes of elderly and high-risk individuals with different vaccination start dates and rollout speeds. MethodsAn agent-based simulation model was adapted and used to project the number of infections, hospitalizations, and deaths under various vaccination start dates, rollout speeds, and prioritization schemes, including (A)no prioritization, (B)two-staged prioritization of elderly population, and (C)multi-staged prioritization of elderly and then high-risk population. The study period was February 18 th , 2020 –June 1 st , 2021, and the state of Georgia was used as a case study. ResultsThe relative effectiveness of the prioritization schemes depends on the outcome considered, as well as the vaccination start date, prioritized subpopulations, and rollout speed. Having no prioritization results in the fewest infections and hospitalizations in most scenarios; however, it yields the highest number of deaths. Prioritizing the elderly and then high-risk individuals results in the fewest overall and high-risk deaths in most scenarios. ConclusionsHaving no vaccine prioritization, i.e., opening vaccination to every adult regardless of age, simplifies vaccine rollout and reduces the infection spread but results in a higher number of deaths, especially among the elderly and high-risk populations. Prioritizing the elderly, then high-risk patients, as opposed to prioritizing only the elderly provides benefit regarding severe outcomes; however, such assumed benefits need to be counterbalanced with challenges in communicating eligibility and criteria and in distributing vaccines effectively and equitably which could result in suboptimal vaccine uptake and coverage, including among people within subpopulations at disproportionate risk of illness, hospitalization and death, of particular concern during periods of high incidence, severe disease, and death.