What is herd immunity?

With the COVID-19 outbreak still under way, it is important to understand the concept of herd immunity. How is it calculated? What does it achieve? Here are some explanations.

Herd immunity occurs when a sufficiently high proportion of a given population is immunized/protected against an infection so that if an infected individual is introduced into the population, the pathogen will no longer spread because it comes up against too many protected subjects. Herd immunity can be obtained by natural infection or by vaccination (if there is a vaccine).

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