vaccīnus

In Latin, vacca means 'cow,' and vaccīnus means 'of or from the cow.' That's the entire etymology of one of the most important words in human history. In 1796, English physician Edward Jenner observed that milkmaids who'd contracted cowpox—a mild disease caught from cows—seemed immune to smallpox, a devastating killer.

Jenner took material from a cowpox blister on a milkmaid's hand and inoculated an eight-year-old boy named James Phipps. When Jenner later exposed the boy to smallpox, he didn't get sick. Jenner called his technique vaccination—from vacca, cow—because the key ingredient came from bovine disease.

The word spread faster than the practice. Vaccination was controversial for decades—critics called it unnatural, dangerous, and blasphemous. Caricaturists drew people sprouting cow parts after being vaccinated. But the results were undeniable, and by the 1800s, vaccination programs were saving thousands of lives annually.

Smallpox was officially eradicated in 1980—the first and only human disease eliminated by vaccination. The technique Jenner pioneered using cowpox has since been adapted for polio, measles, tetanus, influenza, and COVID-19. The Latin word for cow now names the single most lifesaving medical intervention in human history.