The 1721 Smallpox Epidemic in Boston and the Story of Onesimus
In 1721, news of a smallpox outbreak struck fear into the residents of Boston. The disease had arrived on a ship from the Caribbean, and it spread rapidly through the busy colonial port. The first victims were quarantined in a house marked only by a red flag bearing the words “God have mercy on this house.” Hundreds of townspeople fled in panic. Their terror was justified: smallpox was one of the era’s most feared diseases. It was highly contagious, causing high fever, fatigue, and a distinctive crusty rash that often left survivors with permanent scars. In up to 30% of cases, it was fatal. There was no modern medical treatment and little scientific understanding of infectious diseases. This epidemic proved especially devastating. The virus tore through the city, infecting hundreds. Then, an unexpected source offered a potential solution: an enslaved West African man known as Onesimus.
Onesimus and the Practice of Variolation
Onesimus belonged to Cotton Mather, a prominent Puritan minister and intellectual who had played a major role in the Salem Witch Trials. In 1716, Onesimus told Mather that he knew how to prevent smallpox. He explained that he had undergone an operation in Africa: pus from an infected person was rubbed into a small wound on a healthy person. This deliberate exposure gave the recipient a milder form of the disease and, in most cases, lifelong protection. Mather, initially skeptical of his enslaved servant, became intrigued. He verified the account with other enslaved Africans and learned that similar practices existed in Turkey and China. He began advocating for the procedure, known as variolation (or inoculation), as a way to combat the epidemic. Not everyone was receptive. Many colonists resisted a technique associated with Africans. Religious leaders argued it interfered with God’s will. Mather faced fierce backlash: newspapers mocked him, and an explosive device was even thrown into his home. Historian Ted Widmer has noted the racial undertones in much of the opposition.
A Bold Experiment
Despite the controversy, one Boston physician, Zabdiel Boylston, supported the method. During the 1721 outbreak, Boylston inoculated his own son and several enslaved people, then expanded to willing residents. Of the 242 people he inoculated, only six died (roughly 1 in 40). In contrast, among those who caught smallpox naturally, the death rate was about 1 in 7. The epidemic ultimately killed 844 people—more than 14% of Boston’s population. But the success of variolation offered real hope and laid groundwork for future advances in immunization.
Legacy
In 1796, Edward Jenner developed a safer vaccine using cowpox, which eventually replaced variolation. Smallpox vaccination later became mandatory in Massachusetts. Centuries later, in 1980, the World Health Organization declared smallpox eradicated—the only human infectious disease to have been eliminated. Onesimus’s later life remains largely unknown. He partially purchased his freedom from Mather by providing funds for Mather to buy another enslaved person. While history records little else about him, his knowledge helped save hundreds of lives in Boston and contributed to one of medicine’s greatest triumphs. The story of Onesimus highlights how medical knowledge from Africa, Asia, and the Ottoman Empire influenced early Western medicine. Variolation was not unique to any one culture, but his willingness to share this life-saving practice during a deadly crisis made a lasting impact.