Illustration of Benjamin Jesty (1736-1816), English farmer and vaccine pioneer. The idea that infection with cowpox protected against subsequent infections of smallpox was a common folk tale. Jetsy was the first person to test this idea when, during the 1774 smallpox outbreak, he inoculated his wife and sons with liquid from a cowpox lesion a cow's udder. Jetsy performed this inoculation 22 year before Edward Jenner who is widely credited with developing the smallpox vaccine.