title: "Herd immunity": a rough guide.
abstract: 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.
authors.affiliation: Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, United Kingdom. Paul.Fine@Ishtm.ac.uk
authors.forename: Paul
authors.initials: P
authors.lastname: Fine
authors.forename: Ken
authors.initials: K
authors.lastname: Eames
authors.forename: David L
authors.initials: DL
authors.lastname: Heymann
mesh_terms: D003140:Communicable Disease Control; D003141:Communicable Diseases / Q000276:immunology* / Q000635:transmission; D018562:Disease Transmission, Infectious / Q000517:prevention & control*; D006801:Humans; D032521:Immunity, Herd; D009626:Terminology as Topic