The article referenced above is a facinating write-up about early use of vaccinations in America and how George Washington ordered it for his troops.
George Washington struggled against smallpox and the bitter cold to keep his troops alive in Valley Forge. During this time, John Adams lost so many of his troops (1/2) he had to retreat from Quebec. Washington had seen the effects of small pox when he was a teenager visiting the Barbados. He decided to innoculate his troops using a technique indirectly (or partially) learned from slaves who had learned similar treatments in Africa and the technique was also used by the Ottomans. The method used was call variolation which pus from an infection was introduced to the body of the uninfected. Twenty years later, the first true vaccine was developed for small pox by a British scientist, Edward Jenner.
We need to consider the fact that this was an untested technique that could kill you. Imagine the fears of the time, and yet, to some not so small degree, it affected the course of history.