indri Schaelicke | United States
Undoubtedly one of the greatest medical innovations in human history is the invention of the vaccine. The science of vaccination was first seriously pioneered by Edward Jenner in 1796, when he noticed that milkmaids who had caught cowpox before became immune to smallpox later. To test his theory that humans could develop immunity, Jenner took pus from a milkmaid with cowpox and put it into a cut in the arm of an 8-year-old boy. Six weeks later, he inoculated the same boy with smallpox, observing that he did not catch smallpox. Based on his findings, he was able to develop the first vaccines.