Inoculation against smallpox is already a standard practice but involves serious risks.
In 1721, Lady Mary Wortley Montagu had imported variolation to Britain after having observed it in Istanbul, where her husband was the British ambassador.
Voltaire, writing of this, estimated that at this time sixty percent of the population caught smallpox and twenty percent of the population died of it.
Voltaire also stated that the Circassians used the inoculation from times immemorial, and the custom may have been borrowed by the Turks from the Circassians.
In 1765, a Dr. Fewster had published a paper in the London Medical Society entitled "Cow pox and its ability to prevent smallpox", but he had not pursued the subject further.
In the years following 1770, at least five investigators in England and Germany (Sevel, Jensen, Jesty 1774, Rendell, Plett 1791) had successfully tested a cowpox vaccine in humans against smallpox.
For example, Dorset farmer Benjamin Jesty had successfully vaccinated and presumably induced immunity with cowpox in his wife and two children during a smallpox epidemic in 1774, but it is not until Edward Jenner's work some twenty years later that the procedure becomes widely understood.
Edward Jenner, who had earned his MD from the University of St. Andrews in 1792, is also credited with advancing understanding of angina pectoris.
In his correspondence with Heberden, he wrote, "How much the heart must suffer from the coronary arteries not being able to perform their functions."
The initial source of cowpox infection is a disease of horses, called "the grease", which is transferred to cows by farm workers, transforms and then manifests as cowpox.
Noting the common observation that milkmaids are generally immune to smallpox, Jenner postulates that the pus in the blisters that milkmaids receive from cowpox (a disease similar to smallpox, but much less virulent) protects them from smallpox.
He may already have heard of Jesty's success.
