...of the elimination of Smallpox.
http://www.jennermuseum.com/Jenner/finalconquest.html"In 1977 a hospital worker who had nursed a family in a Somali hospital became ill. Ali Maow Maalim had never himself been vaccinated! WHO officials literally sat on his doorstep, letting no one out or in until the last scab had fallen off his last pock. He recovered. He was the last person on Earth to catch smallpox by natural transmission. "
A triumph of modern medicine and an example as to why vaccination is one of the greatest accomplishments of medical science. Polio 'should' have gone this way too, but unfortunately human stupidity has prevented that. Maybe measles and others will be eradicated as well...or maybe not.