In the 1770s an English doctor called Edward Jenner noticed that milkmaids didn’t seem to catch smallpox, the terrifying disease that caused around a third of the people who caught it to die. He thought that their frequent exposure to cowpox, a similar but less severe virus, might be what protected them. In order to test his hypothesis he gave his gardener’s eight-year-old son cowpox and then deliberately infected him with smallpox to see if he had become immune. He had, and Jenner successfully repeated the experiment. “Vaccination”, from the Latin word for cow, soon became commonplace.
It was of course highly irresponsible to expose a child to a deadly disease with no sure knowledge that he would survive. Even so, with hindsight, we can see that the benefits were immense: the vaccine was safe and highly effective. Demonstrating that fact and publicising it encouraged untold numbers of others to follow suit.
