The Impact of Vaccination on Coronavirus Disease 2019 (COVID-19) Outbreaks in the United States

TLDR

Global vaccine development efforts have been accelerated in response to the devastating coronavirus disease 2019 (COVID‑19) pandemic. We evaluated the impact of a 2‑dose COVID‑19 vaccination campaign on reducing incidence, hospitalizations, and deaths in the United States. We used an agent‑based model of SARS‑CoV‑2 transmission, parameterized with US demographics and age‑specific outcomes, to simulate a 2‑dose vaccination campaign with 95% efficacy, 40% coverage, and prioritized high‑risk groups, calibrating to an effective reproduction number of 1.2. The model predicts that the campaign would cut the overall attack rate by ~50%, reduce hospitalizations and deaths by 63–69%, and lower severe outcomes in those 65+ by 54–62%, demonstrating substantial mitigation of COVID‑19 outbreaks while still requiring continued nonpharmaceutical interventions.

Abstract

Global vaccine development efforts have been accelerated in response to the devastating coronavirus disease 2019 (COVID-19) pandemic. We evaluated the impact of a 2-dose COVID-19 vaccination campaign on reducing incidence, hospitalizations, and deaths in the United States.We developed an agent-based model of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission and parameterized it with US demographics and age-specific COVID-19 outcomes. Healthcare workers and high-risk individuals were prioritized for vaccination, whereas children under 18 years of age were not vaccinated. We considered a vaccine efficacy of 95% against disease following 2 doses administered 21 days apart achieving 40% vaccine coverage of the overall population within 284 days. We varied vaccine efficacy against infection and specified 10% preexisting population immunity for the base-case scenario. The model was calibrated to an effective reproduction number of 1.2, accounting for current nonpharmaceutical interventions in the United States.Vaccination reduced the overall attack rate to 4.6% (95% credible interval [CrI]: 4.3%-5.0%) from 9.0% (95% CrI: 8.4%-9.4%) without vaccination, over 300 days. The highest relative reduction (54%-62%) was observed among individuals aged 65 and older. Vaccination markedly reduced adverse outcomes, with non-intensive care unit (ICU) hospitalizations, ICU hospitalizations, and deaths decreasing by 63.5% (95% CrI: 60.3%-66.7%), 65.6% (95% CrI: 62.2%-68.6%), and 69.3% (95% CrI: 65.5%-73.1%), respectively, across the same period.Our results indicate that vaccination can have a substantial impact on mitigating COVID-19 outbreaks, even with limited protection against infection. However, continued compliance with nonpharmaceutical interventions is essential to achieve this impact.