By: Iman Jaffari

Herd immunity, or community immunity, refers to a method of indirect protection against contagious and infectious diseases. It may be achieved through natural infection and recovery or by significant rates of vaccination across a given population.

Herd immunity requires that enough people be infected, such that enough people can later recover and therefore develop antibodies against any recurring infections.[1] Herd immunity is beneficial especially to those who are unable to be vaccinated due to a variety of reasons ranging from auto-immune disorders, age, or lack of access.

Herd immunity first became recognized as a medical phenomenon in 1933 when a substantial number of children began developing immunities to measles followed by a noticeable decline in new cases. This phenomenon occurred after a massive vaccination campaign.[2] Herd Immunity, as a medical concept, further gained prominence in 1977, when it was found that it greatly contributed to the elimination of smallpox.[3] Ever since then, herd immunity has become a proven method in reducing, and often preventing, the spread and proliferation of infectious diseases.

At the onset of the 2019 COVID-19 epidemic, discussions surrounding immunity without a reliable vaccine involved herd immunity as a viable solution. Again, the focus of these discussions by the World Health Organization (WHO) in early 2020 regarded prioritizing the protection and immunity of vulnerable groups who could not be vaccinated. Despite this, the WHO has voiced ethical concerns regarding herd immunity as a viable response to COVID-19.

In a December 2020 white paper, the WHO cautioned that allowing the unmitigated spread of COVID-19 will lead to widespread consequences such as unnecessary deaths and the overcrowding of hospitals and vital health centers.[4] They furthered cautioned against herd immunity by highlighting the lack of current research and understanding about the long-term effects of contracting and recovering from COVID-19. They did not rule out herd immunity as a possible solution but heeded that it required more research before it could be implemented as a viable response to the epidemic.[5]

Nevertheless, herd immunity has a proven track record of reducing new infections of contagious diseases and will continue to be a central topic of discussion and debate in the medical community for years to come.

[1] Centre for Global Health Research, Angus Reid Forum Inc., Unity Health Toronto, University of Toronto, 2020

[2] P, Garnett, Role of Herd Immunity in Determining the Effect of Vaccines, 43 (9): 683–9, February 2005,

[3] M, Leob, “Vaccine herd effect”. Scandinavian Journal of Infectious Diseases, 43 (9): 683–9. September 2011,

[4] World Health Organization General Press, Coronavirus disease (COVID-19): Herd Immunity, Lockdowns and COVID-19, December 2020.

[5] Swaminathan, Soumya, Science in 5, World Health Organization, 28 August 2020