Jenner inoculated an 8-year-old boy using matter from a cowpox sore on the hand of a milkmaid. The boy didn’t feel well for several days, but a later test showed he was resistant to smallpox.

Instead, they caught a mild disease called cowpox. He extracted pus from a cowpox sore and injected it into the arm of an 8-year-old boy. Jenner’s vaccine — or an updated version of it — was ...

Cowpox pustules on the arm of Sarah Nelmes ... The victim would start to experience aches and high fever. Sores would first appear in the mouth and on the tongue, and a rash would spread to ...