Edward Jenner's Life Span Edward Jenner is usually named as the "Pioneer of Immunization." Jenner noticed from observation, that the milkmaids were generally immune to smallpox. He theorized that the the pus in the blisters that milkmaids recieved from cowpox, protected them from smallpox. He tested his theory by exposing James Phipps to a small dosage of cowpox and then Smallpox. James showed no symptoms. (17 mayo 1749 año