Clinical Outcomes Of A COVID-19 Vaccine: Implementation Over Efficacy

Abstract

The global effort to develop a coronavirus disease 2019 (COVID-19) vaccine is on track to produce one or more authorized vaccines. We examine how different definitions and thresholds of vaccine efficacy, coupled with different levels of implementation effectiveness and background epidemic severity, translate into outcomes including cumulative infections, hospitalizations, and deaths. Using a mathematical simulation of vaccination, we find that factors related to implementation will contribute more to the success of vaccination programs than a vaccine's efficacy as determined in clinical trials. The benefits of a vaccine will decline substantially in the event of manufacturing or deployment delays, significant vaccine hesitancy, or greater epidemic severity. Our findings demonstrate the urgent need for health officials to invest greater financial resources and attention to vaccine production and distribution programs, to redouble efforts to promote public confidence in COVID-19 vaccines, and to encourage continued adherence to other mitigation approaches, even after a vaccine becomes available.

Figure 1.. Total Infections: Sensitivity to Vaccine Type

Bar graph representing the fraction of infections averted (vertical axis) under alternative vaccine types -- preventive, disease-modifying, and composite -- and at different background epidemic severities, represented by increasing R_ts. The different shades of each bar represent vaccine efficacies of 25% (darkest), 50% (middle) and 75% (lightest). Blue bars on the left represent an implementation scenario where the vaccination is scaled up in the population at 0.5% per day (pace) with a maximum of 50% coverage. Green bars on the right represent an implementation scenario where the vaccination pace is 1% per day with 90% coverage.

Figure 2.. Total Infections: Sensitivity to Implementation Factors

Nine heat maps, each depicting an individual vaccine type (columns) at a given background epidemic severity (R_t, rows). Base case efficacies (50%) are used for the preventive, disease-modifying, and composite vaccines. Individual maps demonstrate the range of vaccination coverage (horizontal axis, 10-90%) and pace of scale up (vertical axis, 0.1%-2% per day). The color spectrum represents the proportion of infections averted: green averts the greatest number of infections; red the least.