The term vaccination was derived from the Latin word 'vacca' meaning:
The word vaccination originates from Latin feminine noun vacca meaning cow, itself derived from Proto-Indo European root *wokeh meaning cow, reflecting historical link between dairy cattle disease cowpox and protection against smallpox. English physician Edward Jenner in 1796 observed that Gloucestershire milkmaids exposed to cowpox pustules from cow udders developed mild illness but subsequently seemed immune to devastating smallpox epidemics affecting humans. He termed procedure vaccination from vacca to honor bovine source, distinguishing from earlier variolation using smallpox material. La
Ref: Baxby Vaccination etymology; Riedel Proc Baylor 2005 vacca cow Latin; WHO Smallpox history.