The Invention of Vaccines: Edward Jenner and Smallpox

In 1796, English doctor Edward Jenner noticed a local belief that milkmaids who caught cowpox, a usually mild disease, seemed protected from smallpox, one of history’s deadliest infections. He tested the idea by taking material from a cowpox sore on milkmaid Sarah Nelmes’s hand and inoculating eight-year-old James Phipps.James became mildly ill, recovered, and later did not develop smallpox when Jenner tested whether the cowpox exposure protected him. The experiment was ethically unacceptable by modern standards, but it demonstrated the principle behind vaccination: safely training the immune system to recognize a dangerous disease.Jenner did not invent the broader idea of inoculation, earlier practices such as variolation already existed but his cowpox-based method was far safer and became the first successful vaccine. The word “vaccine” itself comes from vacca, Latin for cow.Almost two centuries later, worldwide vaccination campaigns led the World Health Organization to declare smallpox eradicated in 1980, the only human disease ever eradicated globally.