Background: A first generation COVID-19 vaccine is expected to be approved and made available by the end of 2020. While questions of vaccine allocation strategies have received significant attention among scientific and professional healthcare communities, important questions remain regarding the potential impact of the vaccine given uncertainties regarding efficacy against transmission, availability, timing, and durability.Methods: We adapted a susceptible-exposed-infectious-recovered (SEIR) model to examine the potential impact on hospitalization and mortality assuming increasing rates of vaccine efficacy. Specifically, though vaccine efficacy is typically evaluated as reduction in disease, we also evaluated efficacy against infectiousness given the uncertainty of the vaccine to prevent infectiousness as well as potential effects of waning immunity. Furthermore, we evaluated these potential vaccine properties in three US states at different stages of the epidemic to assess the impact on outcomes from distribution timing.Findings: Increased vaccine efficacy against disease reduces hospitalizations and deaths from COVID-19;however, the relative benefit of transmission blocking varied depending on the timing of vaccine distribution. Early in an outbreak, a vaccine that reduces transmission will be relatively more effective than one introduced later in the outbreak. Results from analysis of selected US states further suggest that earlier implementation of a less effective vaccine is more impactful than later implementation of a more effective vaccine. These findings are magnified when considering the durability of the vaccine. Vaccination in the spring will be less impactful when immunity is less durable. Interpretation: Policy choices regarding non-pharmaceutical interventions, such as social distancing and face mask use, will need to remain in place longer if the vaccine is less effective at reducing transmission. In addition, the stage of the local outbreak greatly impacts the overall effectiveness of the vaccine in a region and should be considered when allocating vaccines.Funding: Centers for Disease Control and Prevention (CDC) MInD-Healthcare Program (U01CK000589, 1U01CK000536), James S. McDonnell Foundation 21st Century Science Initiative Collaborative Award in Understanding Dynamic and Multiscale Systems, National Science Foundation (CNS-2027908), National Science Foundation Expeditions (CCF1917819), C3.ai Digital Transformation Institute (AWD1006615), and Google, LLC.Declaration of Interests: The authors declare no competing interests.
Analysis of the Potential Efficacy and Timing of COVID-19 Vaccine on Morbidity and Mortality