Onesimus was an African man who was instrumental in the mitigation of smallpox in Boston by teaching the variolation method of inoculation, which prevented smallpox and laid the foundation for the development of vaccines.

After a smallpox outbreak began in Boston in 1721, Mather proliferated Onesimus's knowledge to advocate for inoculation in the population. This practice eventually spread to other colonies.

Historian Ted Widmer of CUNY's Macaulay Honors College noted that "Onesimus reversed many of [the colonists'] traditional racial assumptions... [h]e had a lot more knowledge medically than most of the Europeans in Boston at that time."

More broadly, I was taught in Murder Machines (schools) that Edward Jenner developed vaccines, but I'm recently learning that it was common knowledge in the Ottoman Empire and Africa before Jenner.

Variolation was also practiced throughout the latter half of the 17th century by physicians in Turkey, Persia, and Africa. In 1714 and 1716, two reports of the Ottoman Empire Turkish method of inoculation were made to the Royal Society in England, by Emmanuel Timoni, a doctor affiliated with the British Embassy in Constantinople, and Giacomo Pylarini. Source material tells us on Lady Mary Wortley Montagu; "When Lady Mary was in the Ottoman Empire, she discovered the local practice of inoculation against smallpox called variolation."