Figure 2.

The Potential Health Burden of COVID-19 if Herd Immunity Is Achieved in the Absence of Vaccination

(A) Relationship between R₀—the basic reproduction number (Box 1)—and the herd immunity threshold, which corresponds to the proportion of individuals in the population that would need be become immune for herd immunity to be established (y axis). As R₀ increases, the proportion of the population that must be immune to generate herd immunity increases (1 – 1/R₀).

(B) Basic reproduction numbers (R₀) and the corresponding herd immunity thresholds for various infectious diseases. R₀ estimates represent the commonly accepted R₀ range for each of the pathogens reported.

(C) Expected number of absolute deaths for the top 20 countries with the highest incidence of COVID-19 as of April 10, 2020, assuming herd immunity is established at a uniform threshold of 67% (R₀ = 3) in each country. Overall COVID-19 infection fatality rates (IFR) of 0.2%, 0.6%, and 1.0% are considered. We note that these numbers are necessarily underestimates given that, even after the herd immunity threshold is reached, it will take a long time until there are no more new cases, and therefore, no new deaths.