When Cotton Mather wasn't busy conducting witch trials back in the day, he doubled as a relatively forward-thinking member of the Royal Society who held to a rudimentary form of the germ theory of disease and supported an attempt to inoculate the population of Boston against a smallpox outbreak.
You can read more about Mather and Zabdiel Boylston, the doctor who actually experimented with and administered the inoculations, in "The Evolution of Preventive Medicine in the United States Army," but you have to scroll down to the Mather/Boylston heading. This site also gives a brief history of the practice of inoculation prior to Mather's time:
Inoculation against smallpox (the insertion into the skin of a normal individual, by scarification or puncture, of material from a fresh lesion of smallpox, with the intention to produce a mild attack of the disease) was an ancient practice of the Chinese and had been utilized in Africa since an uncertain time long past. It came to notice in England about 1700, and in 1714 and 1716, the Royal Society of London published in its "Philosophical Transactions" favorable accounts by Emanuel Timoni, of Constantinople, and Jacobus Pylarini, of Venice. In April 1721, the first inoculation in England was performed on the daughter of Lady Mary Wortly Montagu. Thereafter having been taken up by royalty and found relatively safe and a safeguard, inoculation became widely practiced in England and in Europe. It was applied in the British Army with increasing frequency before the start of the American Revolutionary War.
In a post about the modern fear of vaccination, medical blogger Flea relates an anecdote that I had not heard before. One of Mather's parishioners, who did not take kindly to this new-fangled medical stuff and nonsense, tossed a black powder and turpentine grenade into the reverend's house with the accompanying message:
"Cotton Mather, I was once one of your Meeting; But the Cursed Lye you told of-, you know who, made me leave You, You Dog; And, Damn You I will Enoculate you with this, with a Pox to you."