sigh
herd immunity is not an expression someone in this thread invented you big science guy dude you
Herd immunity (also called
herd effect,
community immunity,
population immunity, or
mass immunity) is a form of indirect protection from
infectious disease that can occur with some diseases when a sufficient percentage of a population has become
immune to an infection, whether through
vaccination or previous infections,
[1] thereby reducing the likelihood of infection for individuals who lack immunity.
[2][3][4] Immune individuals are unlikely to contribute to
disease transmission, disrupting chains of infection, which stops or slows the spread of disease.
[5] The greater the proportion of immune individuals in a community, the smaller the probability that non-immune individuals will come into contact with an infectious individual.
[2]
Individuals can
become immune by recovering from an earlier infection or through vaccination.
[5] Some individuals cannot become immune because of medical conditions, such as an
immunodeficiency or
immunosuppression, and for this group herd immunity is a crucial method of protection.
[6][7] Once the herd immunity threshold has been reached, disease gradually disappears from a population.
[7] This elimination, if achieved worldwide, may result in the permanent reduction in the number of infections to zero, called
eradication.
[8] Herd immunity created via vaccination contributed to the eventual eradication of
smallpox in 1977 and has contributed to the reduction of other diseases.
[9] Herd immunity applies only to
contagious disease, meaning that it is transmitted from one individual to another.
[7] Tetanus, for example, is infectious but not contagious, so herd immunity does not apply.
[6]
Herd immunity was recognized as a naturally occurring phenomenon in the 1930s when it was observed that after a significant number of children had become immune to
measles, the number of new infections temporarily decreased.
[10] Mass vaccination to induce herd immunity has since become common and proved successful in preventing the spread of many infectious diseases.
[11] Opposition to vaccination has posed a challenge to herd immunity, allowing preventable diseases to persist in or return to populations with inadequate vaccination rates.
[12][13][14]
The exact herd immunity threshold (HIT) varies depending on the
basic reproduction number of the disease. An example of a disease with a high threshold is the measles, with a HIT exceeding 95%.
[15]
wiki
the term was first used by a veterinarian
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