An important concept in infectious disease epidemiology, this is the proportion of immune persons in a population, above which the incidence of new cases of a specific infection declines and eventually ceases altogether. This threshold varies according to the characteristics of the infectious pathogen. It is expressed mathematically as
where H is the herd immunity threshold, R0 is the basic reproductive rate, g is the infection transmission parameter, and T is the total population.
Subjects: Public Health and Epidemiology.