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

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

Sarah M Bartsch  1 , Kelly J O'Shea  1 , Marie C Ferguson  1 , Maria Elena Bottazzi  2 , Patrick T Wedlock  1 , Ulrich Strych  2 , James A McKinnell  3 , Sheryl S Siegmund  1 , Sarah N Cox  1 , Peter J Hotez  2 , Bruce Y Lee  4
Affiliations

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

Sarah M Bartsch et al. Am J Prev Med. 2020 Oct.

Abstract

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).

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Figures

Figure 1
Figure 1
Percentage reduction in SARS-CoV-2 cases at the epidemic peak for a vaccine that prevents infection compared with no vaccination, varying with vaccine efficacy, vaccination coverage, R0, and vaccination onset (percentage of population exposed to SARS-CoV-2) occurring when (A) 0% of the population has been exposed, (B) 5% of the population has been exposed, (C) 15% of the population has been exposed, and (D) 30% of population has been exposed.
Figure 2
Figure 2
The total number of SARS-CoV-2 cases averted by vaccination during the course of the epidemic for a vaccine that prevents infection compared with no vaccination, varying with vaccine efficacy, vaccination coverage, R0, and vaccination onset (percentage of population exposed to SARS-CoV-2) occurring when A) 0% of the population has been exposed, B) 5% of the population has been exposed, C) 15% of the population has been exposed, and D) 30% of the population has been exposed.
Figure 3
Figure 3
Percentage reduction in SARS-CoV-2 cases at the epidemic peak and the total number of SARS-CoV-2 cases averted by vaccination during the course of the epidemic compared with no vaccination for (A) a vaccine that reduces viral shedding when vaccination onset occurs when 0% of the population has been exposed to SARS-CoV-2, (B) for a vaccine that prevents infection when asymptomatic cases are as infectious as symptomatic cases when vaccination onset occurs when 0% of the population has been exposed, and (C) for a vaccine that prevents infection when asymptomatic cases are as infectious as symptomatic cases when vaccination onset occurs when 15% of the population has been exposed. R0, reproduction number.
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