Study Estimates How Many Americans Must Be Protected by a Vaccine in Order To Extinguish the COVID-19 Pandemic

A COVID-19 coronavirus vaccine given to 75 percent of the U.S. population must prevent at least 80 percent of infection cases in order to end the COVID-19 pandemic without social distancing measures, according to an AHRQ-funded modeling study published in the American Journal of Preventive Medicine. Researchers created a model that simulated the spread of the COVID-19 virus through the U.S. population. They then simulated administration of vaccinations to different proportions of the population to see what percentage of infection cases would need to be prevented in order to end the epidemic. In an additional scenario, researchers estimated that, if 100 percent of the population receives the vaccine, it will need to prevent at least 60 percent of cases in order to end the pandemic without social distancing measures. Access the abstract.

How Efficacious Must a COVID-19 Coronavirus Vaccine be to Prevent or Stop an Epidemic by Itself

Sarah M Bartsch, Kelly J O'Shea, Marie C Ferguson, Maria-Elena Bottazzi, Sarah N Cox, Ulrich Strych, James A McKinnell, Patrick T Wedlock, Sheryl S Siegmund, Peter J Hotez, Bruce Y Lee

PMID: 32511569
PMCID: PMC7274250
DOI: 10.1101/2020.05.29.20117184

Free PMC article

Abstract

Background: Given the continuing coronavirus disease 2019 (COVID-19) pandemic and much of the U.S. implementing social distancing due to the lack of alternatives, there has been a push to develop a vaccine to eliminate the need for social distancing.

Methods: In 2020, we developed a computational model of the U.S. simulating the spread of COVID-19 coronavirus and vaccination.

Results: Simulation experiments revealed that when vaccine efficacy exceeded 70%, coverage exceeded 60%, and vaccination occurred on day 1, the attack rate dropped to 22% with daily cases not exceeding 3.2 million (reproductive rate, R0, 2.5). When R0 was 3.5, the attack rate dropped to 41% with daily cases not exceeding 14.4 million. Increasing coverage to 75% when vaccination occurred by day 90 resulted in 5% attack rate and daily cases not exceeding 258,029when R0 was 2.5 and a 26% attack rate and maximum daily cases of 22.6 million when R0 was 3.5. When vaccination did not occur until day 180, coverage (i.e., those vaccinated plus those otherwise immune) had to reach 100%. A vaccine with an efficacy between 40% and 70% could still obviate the need for other measures under certain circumstances such as much higher, and in some cases, potentially unachievable, vaccination coverages.

Conclusion: Our study found that to either prevent or largely extinguish an epidemic without any other measures (e.g., social distancing), the vaccine has to have an efficacy of at least 70%.