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Why is the word vaccination connected to the Latin word for cow?

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Infographic showing estimated lives saved by childhood vaccinations worldwide from 1974 to 2024, with syringe-shaped bars for each disease. Measles tops the list at 93.71 million lives saved, followed by tetanus, whooping cough, and others, for a total of 153.84 million lives saved. — vaccine Vaccines and the estimates of lives saved over the period 1974–2024.

The word vaccination is connected to the Latin word for cow because of the pioneering work of the English surgeon Edward Jenner.12

In 1796, Jenner observed that dairymaids who contracted cowpox—a mild disease they caught from cattle—became immune to the deadly smallpox virus. Jenner successfully tested this theory by inoculating a young boy with material from a cowpox lesion, which provided the child with immunity to smallpox.132

Jenner used the term vaccination for this procedure, deriving it from the Latin word vacca, which means "cow". The term is also rooted in the New Latin vaccina (from vaccinus, meaning "of or from a cow"), which appeared in the phrase variolae vaccinae, or "cowpox". This historical connection reflects the origin of the first vaccine, which utilized the cowpox virus to protect humans against smallpox.143