It is estimated that during the eighteenth century, about 60 million Europeans died of smallpox.
The dreaded disease had killed many more than that over the centuries, and those who survived were scarred and often blind.
An old English folk cure was that anyone who had ever had cowpox, a very mild disease caught from cows, would never get smallpox.
Dr. Edward Jenner from England believed that desperate times needed desperate measures.
In 1796, he decided to test the folk cure. First, he injected cowpox fluid into the arm of a healthy eight year old, and the boy soon developed a mild case of cowpox.
Next, he injected smallpox fluid into the arm of the boy and another man, a brave volunteer, who had never had cowpox.
The man contracted smallpox, but the boy did not.
This was the first successful vaccination, but Jenner did not know why it worked.
That discovery would have to wait for Louis Pasteur, nearly 100 years later. Jenner had taken the first step in a long but amazing medical journey.
In 1979, smallpox became the first disease conquered by human beings.
Worldwide vaccination had wiped it out.