The Variola vaccine (which was also the first vaccine made in the world) came from studies carried out by the English physician Edward Jenner. He observed people who became infected by milking cows with a disease of cattle and came to the conclusion that these people were immune to smallpox. The disease, called cowpox, resembled human smallpox by the formation of pustules (lesions with pus).
In view of this observation, in 1796, Jenner inoculated the pus present in a lesion of a milker named Sarah Nelmes, who had the disease (cowpox), in an eight-year-old boy named James Phipps. Phipps acquired the infection mildly and, after ten days, was cured. Later, Jenner inoculated Phipps pus from a person with chickenpox, and the boy suffered nothing. There, the smallpox vaccine was born.
The doctor continued his experiment, repeating the process in more people. In 1798, he reported his discovery in a paper entitled "An Survey on the Causes and Effects of Smallpox Vaccine". Despite facing resistance, in a short time, his discovery was recognized and spread throughout the world. In 1799, the first vaccine institute was created in London and, in 1800, the British Navy began to adopt vaccination.