Herd immunity, also called community immunity, occurs when a sufficient portion of a population is immune to a specific disease, thereby protecting individuals who have not developed immunity. The greater the proportion of a population that is immune or less susceptible to a disease, the lower the probability that a susceptible person will come in contact with an infectious person. If a sufficient number of people (herd) are immune, the infection will no longer circulate.

The benefits of herd immunity apply to various segments of our society: to children too young to be vaccinated, to immunosuppressed patients who cannot be vaccinated, to elderly people who cannot mount an optimal immune response to a vaccine, to people in whom vaccine-induced immunity has waned, to people who have inadequate access to immunizations and to people who remain unvaccinated by choice.

The principle of herd immunity or indirect protection is shown in the...

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