By: Jordan Meadows
Staff Writer
The story of Onesimus, an enslaved African man in 18th-century Boston, is one of perseverance and quiet revolution—whose ripples are still felt today in the global fight against infectious diseases. His knowledge of smallpox inoculation, passed down through generations of Africans, played a pivotal role in introducing the practice of variolation to America. This intervention not only saved lives during a devastating smallpox outbreak in 1721 but also laid the groundwork for the eventual development of vaccines.
Born in Africa—most likely in modern-day Ghana—his exact birthplace and name are unknown. What is clear is that by 1706, he had been forcibly brought to the American colonies as an enslaved person. He was given as a gift to Cotton Mather, a prominent Puritan minister of the North Church in Boston. Mather, a key figure in the Salem Witch Trials, renamed him Onesimus, a name derived from the New Testament, meaning “useful” or “profitable.”
Despite his status as a slave, Onesimus was considered by Whites to be highly intelligent. Mather educated him in reading and writing, skills that were rare among enslaved people at the time.
In 1716, Onesimus shared with Mather a practice from his homeland: inoculation. He explained how he had been deliberately exposed to smallpox in a controlled way, a procedure that would provide lifelong immunity to the disease. The technique, which involved introducing a small amount of infected material into the skin, was already a common practice in many parts of Africa.
At the time, smallpox was one of the deadliest diseases in the world, with no effective treatment. The disease was especially devastating in colonial America, where it ravaged both the settler population and Indigenous communities. Onesimus’s description of the practice struck a chord with Mather, who, despite his deeply ingrained prejudices, recognized its potential.
Mather had learned that the practice of variolation—deliberately infecting a healthy person with a mild case of smallpox to prevent a more serious infection—was not limited to Africa. It had been used in Asia and parts of the Ottoman Empire for centuries.
In 1721, a smallpox epidemic swept through Boston. The disease spread rapidly, killing hundreds and overwhelming the medical community. Mather, having been persuaded by Onesimus’s knowledge, began to advocate for inoculation. However, his efforts were met with intense resistance. Many of Boston’s residents, especially the medical and religious authorities, viewed the practice with skepticism. Some dismissed it as “witchcraft” or “African superstition,” while others saw it as an affront to God’s will, fearing that interfering with divine providence would bring misfortune.
Despite the opposition, Mather persisted in promoting inoculation, enlisting the support of a local physician, Zabdiel Boylston. In 1721, Boylston began the first trial of inoculation in Boston, using the method described by Onesimus. He first inoculated his son and a few enslaved individuals, and then extended the practice to other willing participants.
The results were remarkable. Of the 242 people inoculated, only six died—just 2.5% of those infected. In contrast, the mortality rate among those who were not inoculated was around 14%. Onesimus’s knowledge proved to be a turning point in the battle against smallpox in the colonies.
Although the practice of variolation did not immediately gain widespread acceptance, it ultimately became a vital tool in combating smallpox. The inoculation trials in Boston were followed by similar efforts in other colonies, and by the late 18th century, the method had gained enough traction to influence the development of vaccines. In 1764, John Adams, the future second President of the United States underwent the inoculation. Edward Jenner would later pioneer the smallpox vaccine using cowpox, a much safer alternative to variolation. Over time, the smallpox vaccine became a cornerstone of global immunization efforts.
In 1980, the World Health Organization declared smallpox eradicated—a historic achievement that remains the only instance of the complete eradication of a human infectious disease. The foundation for this victory was laid by Onesimus’s knowledge and the efforts of individuals who believed in him.
While Onesimus’s role in the smallpox inoculation trials is well-documented, little is known about his life after the 1721 outbreak. It is believed that he eventually bought his freedom from Mather. There is no record of Onesimus’s later years, and his ultimate fate remains uncertain. Some historians speculate that he may have left Boston, while others suggest that he continued to work for Mather in some capacity.
Despite the challenges he faced, including personal tragedy (his two young children died before the age of ten), Onesimus’s legacy endured. In 2016, he was posthumously recognized by Boston Magazine as one of the “100 Best Bostonians of All Time”.
Onesimus’s story is a powerful reminder of the often-overlooked contributions of enslaved people to the advancement of science and society. His knowledge of inoculation, passed down through generations of African medical traditions, saved countless lives during a pivotal time in world history and contributed to the eventual eradication of one of the deadliest diseases.
