Vaccine Efficacy Needed for a COVID-19 Coronavirus Vaccine to Prevent or Stop an Epidemic as the Sole Intervention

Am J Prev Med. 2020 Oct;59(4):493-503. doi: 10.1016/j.amepre.2020.06.011. Epub 2020 Jul 15.


Introduction: Given the continuing COVID-19 pandemic and much of the U.S. implementing social distancing owing to the lack of alternatives, there has been a push to develop a vaccine to eliminate the need for social distancing.

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

Results: Simulation experiments revealed that to prevent an epidemic (reduce the peak by >99%), the vaccine efficacy has to be at least 60% when vaccination coverage is 100% (reproduction number=2.5-3.5). This vaccine efficacy threshold rises to 70% when coverage drops to 75% and up to 80% when coverage drops to 60% when reproduction number is 2.5, rising to 80% when coverage drops to 75% when the reproduction number is 3.5. To extinguish an ongoing epidemic, the vaccine efficacy has to be at least 60% when coverage is 100% and at least 80% when coverage drops to 75% to reduce the peak by 85%-86%, 61%-62%, and 32% when vaccination occurs after 5%, 15%, and 30% of the population, respectively, have already been exposed to COVID-19 coronavirus. A vaccine with an efficacy between 60% and 80% could still obviate the need for other measures under certain circumstances such as much higher, and in some cases, potentially unachievable, vaccination coverages.

Conclusions: This study found that the vaccine has to have an efficacy of at least 70% to prevent an epidemic and of at least 80% to largely extinguish an epidemic without any other measures (e.g., social distancing).

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Betacoronavirus / isolation & purification
  • COVID-19
  • COVID-19 Vaccines
  • Communicable Disease Control* / methods
  • Communicable Disease Control* / statistics & numerical data
  • Computer Simulation*
  • Coronavirus Infections* / epidemiology
  • Coronavirus Infections* / prevention & control
  • Disease Eradication / methods
  • Disease Eradication / statistics & numerical data
  • Humans
  • Needs Assessment
  • Pandemics* / prevention & control
  • Pneumonia, Viral* / epidemiology
  • Pneumonia, Viral* / prevention & control
  • SARS-CoV-2
  • Treatment Outcome
  • United States / epidemiology
  • Vaccination Coverage
  • Vaccination* / methods
  • Vaccination* / statistics & numerical data
  • Viral Vaccines / pharmacology*
  • Viral Vaccines / standards


  • COVID-19 Vaccines
  • Viral Vaccines