Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keysNCBI HomepageMyNCBI HomepageMain ContentMain Navigation
Review
. 2020 May 19;52(5):737-741.
doi: 10.1016/j.immuni.2020.04.012.

Herd Immunity: Understanding COVID-19

Haley E Randolph  1 , Luis B Barreiro  2
Affiliations
Review

Herd Immunity: Understanding COVID-19

Haley E Randolph et al. Immunity..

Abstract

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its associated disease, COVID-19, has demonstrated the devastating impact of a novel, infectious pathogen on a susceptible population. Here, we explain the basic concepts of herd immunity and discuss its implications in the context of COVID-19.

PubMed Disclaimer

Figures

Figure 1
Figure 1
Herd Immunity (A) SIR (susceptible, infectious, recovered) model for a completely immunizing infection with an R0 = 4. The model assumes a closed population in which no people leave and no new cases are introduced. Following the introduction of a single infected individual, the proportion of infected individuals (red line) increases rapidly until reaching its peak, which corresponds to the herd immunity threshold. After this point, newly infected individuals infect fewer than one susceptible individual, as a sufficient proportion of the population has become resistant, preventing further spread of the pathogen (orange line). (B) Schematic depiction of the disease propagation dynamics when one infected individual is introduced into a completely susceptible population (top panel) versus a situation in which an infected individual is introduced into a population that has reached the herd immunity threshold (bottom panel). In the naive population, an outbreak quickly emerges, whereas under the scenario of herd immunity, the virus fails to spread and persist in the population.
Figure 2
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.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Anderson R.M., May R.M. Vaccination and herd immunity to infectious diseases. Nature. 1985;318:323–329. - PubMed
    1. Bao L., Deng W., Gao H., Xiao C., Liu J., Xue J., Lv Q., Liu J., Yu P., Xu Y. Reinfection could not occur in SARS-CoV-2 infected rhesus macaques. bioRxiv. 2020 doi: 10.1101/2020.03.13.990226. - DOI
    1. Callow K.A., Parry H.F., Sergeant M., Tyrrell D.A. The time course of the immune response to experimental coronavirus infection of man. Epidemiol. Infect. 1990;105:435–446. - PMC - PubMed
    1. Delamater P.L., Street E.J., Leslie T.F., Yang Y.T., Jacobsen K.H. Complexity of the basic reproduction number (R0) Emerg. Infect. Dis. 2019;25:1–4. - PMC - PubMed
    1. The Centre for Evidence-Based Medicine . 2020. Global COVID-19 case fatality rates.https://www.cebm.net/covid-19/global-covid-19-case-fatality-rates

Publication types

LinkOut - more resources

close