[ad_1]
Herd immunity offers indirect protection to people susceptible to an infectious disease
The herd immunity threshold is the minimum proportion of the population that must be immunized against an infectious disease, usually due to vaccination, for the incidence of the disease to remain stable or to decrease.1
The herd immunity threshold correlates with the infectivity of the pathogen
The herd immunity threshold against measles, one of the most infectious diseases, is around 94%.1 For SARS-CoV-2 variants of concern, such as B.1.1.7 (Alpha), the cutoff is around 80%2 and it may be higher for new emerging variants like B.1.617.2 (Delta).3
Effective vaccines with long-lasting protection are essential for achieving herd immunity
Vaccines are not perfect, and some vaccinated people can still be infected and transmit SARS-CoV-2.4 People who are immunocompromised may not develop an adequate immune response. Epidemics can occur despite high vaccination coverage in the population. The effectiveness varies depending on the type of vaccine, the number of doses administered and the particular variant of SARS-CoV-2 in circulation. Based on estimates of the efficacy of 2 doses of vaccine against symptomatic B.1.1.7 (Alpha) infection in Ontario (90% efficacy), up to 90% vaccine coverage in the population may be required. for collective immunity.5 The increase in the prevalence of more infectious variants and the reduction in vaccine effectiveness against them would require even higher coverage. The duration of immunity against infection or vaccination is currently unknown.4
Vaccination hesitation and structural barriers to vaccination can threaten herd immunity
High and uniform immunization coverage is necessary to achieve herd immunity. Obtaining sufficient vaccination coverage depends on combating vaccine resistance and obstacles to vaccination which can lead to pockets of sensitivity.
Maintaining collective immunity requires sustained efforts
Maintaining herd immunity will depend on the effectiveness of the variant vaccines, removing barriers to vaccination, and maintaining coverage if repeat vaccination is required and as the population changes (for example, due to births, immigration). Even if herd immunity is not achieved, high immunization coverage will dramatically reduce morbidity and mortality rates and ease the burden of COVID-19 on Canada’s health systems.
Footnotes
-
Competing interests: Shelly Bolotin reports funding from the Canadian Institutes of Health Research, the Canadian Immunization Research Network, the COVID-19 Immunity Working Group and the Public Health Agency of Canada, in outside of submitted work. She is a member of the Canadian Immunization Research Network Management Committee, COVID-19 Immunity Working Group Leadership Group. The authors are employees of Public Health Ontario; this organization paid the cost of processing the item. No other competing interests were declared.
-
This article has been peer reviewed.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY-NC-ND 4.0), which permits use, distribution and reproduction in any medium, provided that the original publication is properly cited, the use is not commercial (that is, for research or teaching purposes), and no modifications or adaptations are made. See: https://creativecommons.org/licenses/by-nc-nd/4.0/
|
Sources 2/ https://www.cmaj.ca/content/193/28/E1089 The mention sources can contact us to remove/changing this article |
[ad_2]