The acceptance of vaccines against disease is routine procedure, but many people are unaware that the origin of the word is connected cows. The word vaccine derives from vacca, which is Latin for cow. During the late 18th century, physicians noticed that farmers and farmworkers who worked with cows seldom contracted smallpox. At that time, smallpox was one of the most deadly diseases in the world for which there was no known cure. The apparent immunity of those who worked closely with cows came to the notice of English physician Edward Jenner (1749-1822). Like other physicians at the time, Jenner knew that cows regularly developed a viral rash, which formed on their teats in the form of vesicles. From the cows’ teats, the rash, known as cowpox, was passed on to humans but it was harmless. With minimal treatment, it was also quite harmless to cows. This led Jenner to hypothesise that humans exposed to cowpox might also be immune to smallpox. He was right. Jenner had not only discovered a way of preventing one of the most deadly diseases on the planet, but also pioneered a major revolution in medicine, the prevention of disease through vaccines. Jenner is credited with coining the words, vaccine (1799), vaccination (1800) and vaccinate (1803).