The word vaccine comes from the word cow. In the 18th century, cows were decimated by an infectious disease called cowpox, or vaiola vaccina in Latin. The illness could also be passed onto humans. But English doctor Edward Jenner noticed that people who were in regular contact with cows (and therefore the virus itself) didn’t seem to get cowpox when epidemics were raging elsewhere. That’s how the concept of a vaccine was born! The cowpox virus was injected into humans in very small doses to immunise them against the disease.