Edward Jenner, born in mid-18th century England, would eventually become one of the most famous scientists in medical history and the so-named “Father of Immunology.” After observing that cowpox infection seemed to protect humans against smallpox, Jenner inoculated an eight-year-old boy with cowpox matter from a blister on the hand of an English milkmaid. He then repeatedly attempted to “challenge” the cowpox inoculation by exposing the boy to smallpox material—but the boy never fell ill. Jenner had demonstrated smallpox immunization.

Jenner’s method of vaccination against smallpox grew in popularity and eventually replaced variolation, which had been the standard before his demonstration. In the latter part of the 20th century, about 150 years after Jenner’s death in 1823, smallpox would be making its last gasps. It would eventually be eradicated after a massive surveillance and vaccination program—thanks largely to the initial efforts of the Father of Immunology.

Sources consulted for this timeline

Edward Jenner’s Later Years. The Edward Jenner Museum. Available at: http://www.jennermuseum.com/Jenner/edwardjenner%27sla.html.
Plotkin SA, Orenstein WA, Offit PA, eds. Vaccines, 5th ed. Philadelphia: Saunders, 2008.