vaccine (n.)
A vaccine is a preparation that trains the body against a disease. The word comes from the Latin vacca, cow.12
Edward Jenner’s report of 1798 was an inquiry into the Variolae vaccinae, the pustules of the cow: his term for cowpox. People who had caught cowpox, usually from milking, turned out to be protected against smallpox.1
The method spread and the name went with it. Vaccines are made in many ways now and almost none of them involve a cow, but the word still says where the first one was found.12
The vaccine was given in two doses.