herd immunity








noun

  1. the immunity or resistance to a particular infection that occurs in a group of people or animals when a very high percentage of individuals have been vaccinated or previously exposed to the infection.

n.

  1. Resistance to the spread of infectious disease in a group because susceptible members are few, making transmission from an infected member unlikely.
  2. The immunologic status of a population, determined by the ratio of resistant to susceptible members and their distribution.
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