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What Do Cows Have to Do with Vaccines?

Painting of Edward Jenner.
Painting of Edward Jenner. Credit: Courtesy of the National Library of Medicine

The word “vaccine” comes from the Latin word vaccinus, which means “pertaining to cows.” What do cows have to do with vaccines? The first vaccine was based on the relatively mild cowpox virus, which infected cows and people. This vaccine protected people against the related, but much more dangerous, smallpox virus.

More than 200 years ago, Edward Jenner, a country physician practicing in England, noticed that milkmaids rarely suffered from smallpox. The milkmaids often did get cowpox, a related but far less serious disease, and those who did never became ill with smallpox. In an experiment that laid the foundation for modern vaccines, Jenner took a few drops of fluid from the skin sore of a woman who had cowpox and injected the fluid into the arm of a healthy young boy who had never had cowpox or smallpox.

Six weeks later, Jenner injected the boy with fluid from a smallpox sore, but the boy remained free of smallpox. Dr. Jenner had discovered one of the fundamental principles of immunization. He had used a relatively harmless foreign substance to evoke an immune response that protected someone from an infectious disease. His discovery would ease the suffering of people around the world and eventually lead to the elimination of smallpox, a disease that killed a million people, mostly children, each year in Europe. By the beginning of the 20th century, vaccines were in use for diseases that had nothing to do with cows—like rabies, diphtheria, typhoid fever, and plague—but the name stuck.

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Last Updated March 09, 2009