"Herd immunity": a rough guide

Clin Infect Dis. 2011 Apr 1;52(7):911-6. doi: 10.1093/cid/cir007.


The term "herd immunity" is widely used but carries a variety of meanings. Some authors use it to describe the proportion immune among individuals in a population. Others use it with reference to a particular threshold proportion of immune individuals that should lead to a decline in incidence of infection. Still others use it to refer to a pattern of immunity that should protect a population from invasion of a new infection. A common implication of the term is that the risk of infection among susceptible individuals in a population is reduced by the presence and proximity of immune individuals (this is sometimes referred to as "indirect protection" or a "herd effect"). We provide brief historical, epidemiologic, theoretical, and pragmatic public health perspectives on this concept.

Publication types

  • Review

MeSH terms

  • Communicable Disease Control
  • Communicable Diseases / immunology*
  • Communicable Diseases / transmission
  • Disease Transmission, Infectious / prevention & control*
  • Humans
  • Immunity, Herd*
  • Terminology as Topic