Vaccination and the Germ Theory Revolution

The practice of vaccination began with the English physician Edward Jenner, who observed that milkmaids who had contracted the relatively mild disease cowpox seemed to be protected from the far more dangerous smallpox. In May 1796, Jenner tested this observation by inoculating an eight-year-old boy, James Phipps, with material taken from a cowpox lesion on the hand of a milkmaid, Sarah Nelmes; when he later exposed the boy to smallpox matter, Phipps did not develop the disease. Jenner published his findings in 1798 in a work titled An Inquiry into the Causes and Effects of the Variolae Vaccinae, and the term "vaccine," from the Latin vacca, meaning cow, entered medical language to describe this new method of protection. Although the practice of inoculation with smallpox material itself (variolation) predated Jenner, his use of the safer cowpox virus, and his systematic demonstration of its protective effect, marked the beginning of modern vaccination and, ultimately, the eventual eradication of smallpox nearly two centuries later.