Onesimus: The enslaved African who introduced inoculation to the United States


Onesimus – the Black slave who introduced inoculation to save Bostonians from smallpox. Image: A slave being taken aboard a ship

On April 22, 1721 a ship from the Caribbean arrived in Boston carrying a sailor with smallpox. Though he was quarantined, it didn’t prevent a smallpox outbreak from ravaging the colonial town of Boston, Massachusetts.

With rising death tolls, Bostonians were running out of solutions to curb the epidemic. That is, until a New England Puritan clergyman named Cotton Mather stepped forward with an unusual treatment plan called inoculation. Initially met with hostility and resistance, the practice eventually saved the lives of many Bostonians and laid the foundation for the development of vaccines.

But it wasn’t Mather that discovered inoculation. Rather, it was his slave Onesimus who first shared with his master how he had survived smallpox back in Africa. For many years, Onesimus wasn’t credited for introducing inoculation to the United States. However, the modern world now recognizes and acknowledges him as the father of vaccination.

Here’s more about Onesimus, the slave that saved Boston:

The Early Life of Onesimus: Birth, Enslavement & Personal Life

Much of Onesimus’ life in Africa remains largely unknown. Based on the descriptions his master, Puritan clergyman and writer Cotton Mather (1663-1723), described, he was likely of Garamante descent, located in southern Libya, or of Coromantee descent, located in modern-day Ghana in West Africa.

The earliest record of Onesimus was found in 1706 when he arrived in North America. Towards the end of the year, he was given to Mather as a gift. Mather was a Puritan minister and had earlier played a prominent role in the Salem Witch Trials (1692-1693) that had occurred in the Massachusetts colony. He had written extensively about witchcraft and spirituality and defended the trials.

Upon receiving the slave from his congregation, Mathers renamed him Onesimus, which means “useful” or “helpful”. He named him after the Holy Apostle Onesimus, who was a first century AD slave in the Byzantine Empire. Onesimus certainly lived up to that name, and according to Mathers, the young slave displayed signs of intelligence. He also learned how to read and write. However, the slave owner remained wary of his slave due to Onesimus’ choice of worship. In his diary, Mather wrote that his slave practiced “devilish rites.”

Onesimus earned a living while working for Mather. As a result, he was able to buy a house for himself and his family. It’s not known if his wife was a freed slave during that time. The couple had two children, Onesimulus and Katy, who both died before the age of 10.

Onesimus was not a Christian, and Mather tried to convert him to Christianity after the death of his children. However, Onesimus rejected the offer, and Mather took offense under the belief that he had failed as a minister to convert an unbeliever. The minister tried again, this time attempting to convert Onesimus but failed yet again. Mather described his slave’s behavior as “stubborn” in his diary.

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Did you know…?

Onesimus’ master Cotton Mather (1663-1723) wielded a lot of influence in colonial Boston. Historians have cited Memorable Providences, a 1689 work written by Puritan clergyman Cotton Mather, for contributing in fueling the hysteria during the Salem witch trials. Mather’s book claimed to have detailed information about the typical signs people should take note in order to identify a demonic possession. His book was devoid of any scientific or natural explanations for the hysterical fits that alleged possessed persons experienced.

Onesimus teaches inoculation

When Onesimus joined the Mather household as a slave, Mather inquired about a scar on his forearm. It was there that the slave described the process of smallpox inoculation. At that time, the practice was relatively unknown in the Americas but was largely performed by tribes in Africa and Asia. In China, for example, inoculation had existed as far back as 1,000 BC. It was also widely practiced during the age of the Ottoman Empire.

New England Puritan clergyman and writer Cotton Mather

According to Onesimus, pus was drawn out of the pustules of an infected person and applied onto the broken skin of an uninfected person. The uninfected person would then experience a mild reaction and later build immunity against the disease. Mather wrote in his report: “People take Juice of Small-Pox; and Cutty-skin, and Putt in a drop.” It is believed that Onesimus had been inoculated long before leaving Africa, especially since it was common practice on the continent back then.

Mather took Onesimus’ advice seriously. He also believed that diseases like smallpox were spiritual illnesses; therefore, he deemed a cure as “God’s providential gift.” He also figured that by sharing the cure, he would be recognized in society, effectively reinstating religion back into politics.

Cotton Mather explaining to the Royal Society of London how he was introduced to inoculation by Onesimus

The Boston Smallpox Epidemic

Boston in 1721 was a growing town with a population of more than 10,500. But the town wasn’t well planned, so it was overpopulated and dirty. The unclean environment made it the perfect breeding ground for diseases to spread.

On April 22, a ship arrived at the Boston Harbor from the Caribbean carrying a sailor who had contracted smallpox. Even though his condition had been detected early and he was quarantined, the disease still managed to spread rapidly into the town.

The disease ravaged all of Boston from 1721 to wintertime 1722. Patients suffered from fever, extreme tiredness, and rashes that caused severe scarring. Close to half of the population contracted the disease, which killed about 850 people died. These casualties were among some of the highest during the 18th century.

At the height of the Boston smallpox epidemic, Mather’s assistance was sought by the public, especially since they saw him as a leader. He shared Onesimus’ process of inoculation to the people. At first, his suggestions were rejected, particularly because the people didn’t trust the source i.e., Onesiumus. The whites felt that the black slaves would stage a revolt against their white owners during that moment of weakness. They were under the assumption that Onesimus was planning to poison them. Mather himself experienced fierce resistance. The newspapers wrote negatively of him, and there was a grenade and other lethal projectiles thrown into his home. The people that threw the grenade demanded that he inoculate his own son first.

However, they eventually adopted the practice when they ran out of solutions. A doctor named Zabdiel Boylston tested Onesimus’ theory on his son and two other slaves. Only then did the rest of Boston’s white society accept inoculation. But not before embarking on protests against Boylston. The doctor was even imprisoned for spreading the disease. About two hundred and forty-two (242) were inoculated, and out of them, only six people died. Although the statistics were not entirely impressive, it was significantly better than the death rates before inoculation.

How did Onesimus transform the medical world?

By sharing the inoculation technique with Mather, which eventually saved the lives of many Bostonians, Onesimus laid the foundation for vaccinations. Years later, in 1796, an English scientist named Edward Jenner (1749-1843) used the slave’s inoculation theory and developed the world’s first vaccine – the smallpox vaccine.

Jenner’s smallpox vaccine used cowpox, which was closely related to smallpox, to provide immunity against the disease. Eventually, vaccination and inoculation became more mainstream, and by 1809, residents of Massachusetts were legally required to be vaccinated or inoculated.

By 1980, smallpox was fully eradicated. According to the World Health Organization, it was the first modern disease to have been completely eradicated.

Known as “the father of immunology”, English scientist and physician Edward Jenner (1749-1843) is credited with developing the world’s first vaccine – the smallpox vaccine. Undoubtedly, Jenner, who was also the physician of King George IV, derived some bit of inspiration from the inoculation procedure Onesimus used in Boston.

Why was Onesimus’ contribution whitewashed?

Sadly, Onesimus’ solution to the Boston smallpox epidemic was whitewashed as the years passed. White slave owners wrote that it was Mather, who first established the theory of vaccination in the Americas. Boylston was also credited for introducing inoculation to America, as written on his tomb. Fortunately, Onesimus’ story came to life thanks to historians like Henry Louis Gates and Thomas H. Brown, who shed light on the contributions of Black Americans in US history.

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Was Onesimus ever freed?

Five years before the smallpox outbreak, in 1716, Onesimus tried to purchase his freedom. Mather agreed but only after Onesimus agreed to the terms and conditions.

In those terms, Onesimus was still required to work for the Mather family and also return five pounds that he had allegedly stolen from his master. Mather wrote that Onesimus had a “thievish” behavior and the slave he had considered useful was now useless.

It’s not really clear what caused the deterioration of the relationship between Onesimus and Mather. For some, it was the alleged theft, but for many other suggestions, it might have been Mather’s failure in attempting to convert his slave to Christianity.

Eventually though, Onesimus bought his freedom. Not much is known of his life afterwards, but the legacy he left behind saved the lives of many people all over the world.


For a long time, Onesimus did not get the credit that he deserved for his contributions and inoculation methodology

Celebrating Onesimus

Today, Onesimus is regarded as the father of vaccination, and in 2016, he was featured in Boston magazine’s “Best Bostonians of All Time”, in the 52nd position. He will be remembered for being one of the leading pioneers in medical science.

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