Word Origin & History
1803, used by British physician Edward Jenner for the technique he devised of preventing smallpox by injecting people with the cowpox virus (variolae vaccinae), from vaccine (adj.) "pertaining to cows, from cows" (1798), from L. vaccinus "from cows," from vacca "cow" (bos being originally "ox," "a loan
word from a rural dialect" according to Buck, who cites Umbrian bue). "The use of the term for diseases other than smallpox is due to Pasteur (Trans. 7th Session Internat. Med. Congr. (1881) I.90)" [OED].