First modern vaccination

The first modern vaccinations were performed by British doctor Edward Jenner in 1796. During his career, Jenner noticed that dairy workers were often resistant to the highly lethal and contagious smallpox disease, and postulated that this was a result of their having previously contracted and recovered from far less harmful cowpox. He put this theory to the test in May 1796 by infecting eight-year-old James Phipps with cowpox, then several weeks later with smallpox; the subject did not develop smallpox, which Jenner concluded formally proved the efficacy of vaccinations. Although initially Jenner's ideas met with resistance, he persisted until the scientific community took his findings on board; he coined the word "vaccine" in a paper published in 1798. His work with vaccines revolutionized a field of medicine that has gone on to prevent countless deaths.

A more primitive form of inoculation, called "variolation", had been in use since the 10th century. It exposed healthy people to infected tissue in order to reduce their risk of contracting diseases such as smallpox, but is not considered a true "vaccination". In the 18th century, there are also accounts of others using cowpox to try to immunize against smallpox. However, Jenner was the first person to formalize the procedure and to present his findings to the medical community.