In the history of Smallpox and Vaccination, Edward Jenner carried out the first vaccination around 1800 then passed the vaccine to Dr. John Haygarth who subsequently did to professor Benjamin Waterhouse who promoted vaccination in New England and then convinced Thomas Jefferson to try it and so on...So Jenner's achievement is yet relevant these days.
The event occurring first in the historical timeline is that "Smallpox survivors were recognized to form immunity to the disease".