Edward Jenner, British physician, c 1809.

UNITED KINGDOM - JUNE 28: Engraving by W H Mote after a work by Sir Thomas Lawrence. Jenner (1749-1823), an English doctor and pupil of John Hunter, introduced fluid from a cowpox sore through a person's skin, in order to inoculate them against smallpox, a similar but more dangerous disease. He called his method 'vaccination' from 'vacca', the Latin word for cow. Although his discovery pre-dated any scientific explanation, his research, published as 'Inquiry into the Cause and Effects of Variolae Vaccinae [cow-pox]' in 1798, showed that using fluid from a human with cowpox was safer than variolation; inoculating non-infected people with fluid from pustules of smallpox. The 1853 Vaccination Act heralded an era of compulsory vaccination against smallpox. (Photo by SSPL/Getty Images)