Herd immunity is a form of indirect protection that applies only to contagious diseases. It occurs when a sufficient percentage of a population has become immune to an infection, whether through previous infections or vaccination, thereby reducing the likelihood of infection for individuals who lack immunity.
A cow with rinderpest in the "milk fever" position, 1982. The last confirmed case of rinderpest occurred in Kenya in 2001, and the disease was officially declared eradicated in 2011.
Measles vaccine coverage and reported measles cases in Eastern Mediterranean countries. As coverage increased, the number of cases decreased.
In biology, immunity is the state of being insusceptible or resistant to a noxious agent or process, especially a pathogen or infectious disease. Immunity may occur naturally or be produced by prior exposure or immunization.
A representation of the cholera epidemic of the 19th century
Louis Pasteur in his laboratory, 1885, by Albert Edelfelt
One of the first bottles of diphtheria antitoxin produced (dated 1895)
Poster from before the 1979 eradication of smallpox, promoting vaccination