“At first, all agreed with Jenner, that one vaccination protected a person for life, against small-pox ; this, however, was soon found to be untrue. Then, one thorough vaccination in infancy and one after puberty, were deemed necessary. This also proved a delusion. Its advocates next advised the practice to be repeated at maturity, and finally it was thought necessary to assure perfect immunity, that vaccination should be repeated every three or four years.” — Robert A. Gunn, Vaccination: Its Fallacies and Evils, around 1877
