What animal for which the word vaccine is named?

The word "vaccine" is derived from the Latin word "vacca," which means "cow." This is because the first vaccine was developed to protect against cowpox, a disease that affects cattle. The vaccine was created by Edward Jenner in 1796, and it was based on the observation that milkmaids who had been exposed to cowpox were immune to smallpox, a deadly disease that was common at the time. Jenner hypothesized that exposure to cowpox provided protection against smallpox, and he tested this by deliberately infecting a young boy with cowpox and then later exposing him to smallpox. The boy did not develop smallpox, demonstrating that the cowpox vaccine was effective.