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Herd immunity
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Herd immunity, also called population immunity, is indirect protection against an infectious disease. It arises when a population is immune, either because people were vaccinated or because they developed immunity after having the infection earlier.
A vaccinated person is protected from getting sick and also from passing the pathogen, the germ that causes the disease, on to someone else. That breaks the chains of transmission, the paths an infection follows from one person to the next. It's like a row of dominoes with a few pulled out of the middle: the one that falls can no longer reach the ones after it.
That matters for people who cannot be vaccinated, for example because they are allergic to the vaccine. One of the goals of herd immunity is to keep those vulnerable groups protected from the disease even though they cannot get the vaccine themselves.
In brief
Herd immunity, also called population immunity, is the indirect protection against an infectious disease that arises when a population is immune, through vaccination or prior infection.
Vaccinated people are protected from catching the disease and from transmitting the pathogen, which breaks chains of transmission.
Infection spreads like a chain, and each immune person is a broken link.
One of its goals is to protect vulnerable groups who cannot be vaccinated, for example because of a vaccine allergy.
Sources (1)
- World Health OrganizationCoronavirus disease (COVID-19): Herd immunity, lockdowns and COVID-19, WHOPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
Updated