Vaccine

The  medical term [vaccine] originates from the Latin term [vacca] meaning "cow". The Latin adjectival form is [vaccinus].

The word originated from the work of Edward Jenner (1749 - 1823) who, based in observation, developed an injection of cowpox virus and injected them into patients, rendering them inmune to smallpox. This extraordinary discovery was the basis for the Balmis Expedition to the New World.

Since the cowpox virus was extracted initally from cows (Lat:vacca), and later from human cowpox sores, and Latin was at the time the preferred language of medical communication, the word "vaccina" was created. Evolution of the word led to the English [vaccine] and Spanish [vacuna]