Edward Jenner (1749-1823) was a country doctor who studied medicine in London. As a doctor he had vaccinated patients against smallpox. Working in the country, Jenner heard milkmaids didn’t catch smallpox and set out to know why. He discovered that they did catch cowpox (a much milder disease than smallpox) and reasoned that this must make them immune to smallpox. He experimented and proved this true, calling his new idea vaccination.