Smallpox

It was on this day in 1796, that Edward Jenner, a doctor, inoculated an eight-year-old boy with a vaccine for smallpox. It was the first safe vaccine ever developed, and it was the first time anyone had successfully prevented the infection of any contagious disease. What made it so remarkable was that it was accomplished before the causes of disease were even understood, decades before anyone even knew about the existence of germs.

Jenner was a country doctor. He studied for a few years in a hospital in London, and learned something about the scientific method. Smallpox at the time was the most devastating disease in the world. It caused boils to break out all over the body, and killed about one in four adults who caught it, and one in every three children. It was so contagious, most people who lived in populous areas caught it at some point in their lives.

From The Writer’s Almanac, which has more.

Update May 15: There’s another story on the origins of smallpox vaccination at hedgeblog.