How an Enslaved Man Helped Boston Battle a Devastating Disease 300 Years Ago

Onesimus' testimony of his safe inoculation went on to save colonial Boston from smallpox and eventually led to the development of the first vaccine

A view of Boston Harbor around 1720
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Three hundred years ago, Boston was in the midst of another deadly health crisis: the spread of smallpox.

In the 1721 smallpox epidemic, the disease infected more than half of the city and led to the death of 850 people -- nearly 8% of Boston's population.

That smallpox outbreak, one of many Boston faced in its early years, led to the introduction in what is now known as inoculation, a medical advancement that saved many lives. It is also a forerunner to the vaccines central to the fight against COVID-19 today, experts say.

Often overlooked in the history of that inoculation is an enslaved man who had been brought to Boston named Onesimus, according to experts.

Inoculated against smallpox in Africa, Onesimus testified that purposely infecting a person with a disease protected them against dying from the virus. It was vital in starting the first smallpox inoculations in Boston.

The episode "is important for the history of public health and scientific innovation [and] important for the history of race relations," Harvard history of science professor David S. Jones said.

Yet Onesimus' role in Boston's first inoculations was for years less well-known than the man who owned him, the influential preacher Cotton Mather, famous for his role in the Salem witch trials.

OrigiNation Cultural Arts Center of Boston gives a moving performance in honor of Black History Month.

This account is based on what little historical record exists of Onesimus, scholarly articles about the history of inoculation, a Harvard Medical School review of the history and interviews from historians who have studied public health and colonial America.

'He described the operation to me, and showed me in his arm the scar'

While few details about Onesimus' life are known, Jones said that he was given as a gift to prominent Puritan minister Cotton Mather by Mather's congregation.

“The whole notion that a congregation would give its minister as a present an enslaved person is testimony to the rotten world in which all these people inhabited, but Mather describes him as a pretty intelligent fellow,” Jones said.  

Mather, an influential figure in the Salem witch trials, was trying to find a way to fight smallpox, a disease that had devastated New England in waves in the 1600s and 1702, according to a journal article written by epidemiologists at Case Western Reserve University. He turned to the practice of inoculation — infecting people with a weakened form of the disease to allow their bodies to create a resistance to it through what we now know as antibodies, which he had first discovered through Onesimus.

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Portrait of Cotton Mather, famous New England Puritan minister. (Photo by © CORBIS/Corbis via Getty Images)

Successful cases of inoculation had already appeared in Turkey, China and India by 1721. The scientific journal Philosophical Transactions of the Royal Society published some of these accounts, including Mather’s own search for a cure for smallpox, wrote Arthur Boylston, a former professor of pathology at the University of Leeds, in the Journal of the Royal Society of Medicine.

Onesimus had been inoculated in his native West Africa, according to LaShyra Nolen, a student at Harvard Medical School who has researched Onesimus. He served as "living proof" that inoculation worked for the influential Mather.

In a letter cited by Bolyston, Mather credited his belief in inoculation to Onesimus, writing that Onesimus “had undergone an operation, which had given him something of the smallpox and would forever preserve him from it.” 

“He described the operation to me, and showed me in his arm the scar which it had left upon him,” Mather wrote. 

Onesimus’ testimony led to one of the first known smallpox inoculation campaigns in American history during the 1721-1722 epidemic in Massachusetts, according to Harvard Medical School account of the outbreak. At Mather’s urging, Dr. Zabdiel Boylston inoculated his own son, Mather’s son and 285 other Bostonians. (Read a contemporary account here.)

Of the 287 people who were inoculated, only 2% of them died, a Massachusetts state epidemiologist wrote in 1921 in the forerunner to The New England Journal of Medicine. More than 14% of the people who were not inoculated and contracted smallpox died, a much larger portion of the 850-person death toll. And in the years that followed, inoculations increased in Boston while "natural" smallpox infections, ones not caused by inoculation, fell dramatically.

Instances of inoculation such as the Boston trial paved the way for Edward Jenner, an English physician, to develop the first vaccine for smallpox in 1796. It was the world's first immunization.  

Some of the first people included in Mather's smallpox inoculation experiment in Boston were enslaved adults and their children, Reed College history professor Margot Minardi said. She noted that, while they weren't the only test subjects in the inoculation trial, the people in slavery likely could not decline.

The trial proved to be successful, but she said in an email it was an early instance of a trend: “This inoculation trial is thus one of the many instances in American medical history where medical experimentation was done on people of color who didn't necessarily have a say in what was done to their bodies.”

Not all Bostonians agreed with the practice of inoculation, especially because the idea originated with an enslaved man. Dr. William Douglass, one of the only physicians in Boston to hold a medical degree at the time, lambasted Mather for spearheading the untested practice.

“The Boston community had a mixed assessment of whether or not you could trust someone like Onesimus, either as an authority of scientific knowledge or public health knowledge,” Jones said. 

The public backlash to inoculation was so fierce that someone threw a small bomb through Mather's window, according to the Harvard Medical School account of the smallpox epidemic that covers Onesimus and Mather. It had a message attached: “Cotton Mather, you dog, dam you! I’ll inoculate you with this; with a pox to you."

Remembering Onesimus

Despite Onesimus’ contributions to Boston and the development of the vaccine, his presence was for centuries overlooked in medical history. In 1932, Dr. Samuel Bayard Woodward said in a speech to the Massachusetts Medical Society that the idea of inoculation “came then from Cotton Mather and from Cotton Mather only.” 

Onesimus’ story is similar to others who contributed to medical discoveries and were overlooked because of their race, Minardi said. To this day, there are no images of Onesimus in the Library of Congress, but several of Cotton Mather.

“I would say that one thing to learn from Onesimus's story is that medicine advances thanks to the knowledge, labor, and experience of people... often go unrecognized due to racial and other biases,” she wrote. 

Jones said this erasure stems from a “bias that science is something that white people do.” This bias can lead to confusion about who exactly brought inoculation to Boston, ignoring Onesimus' impact entirely on the 1721 epidemic, he added.

“For the past 20, even 30 years, there has been a major effort by historians in general and historians of science and medicine, to look for those lost histories of how non-American, non-European people did actively contribute to the production of knowledge,” Jones said. 

Jones said that past historians who were less attentive to the stories of enslaved people erased Onesimus's story, but since 2000, there has been an increase in scholarly articles and media coverage about him. In 2016, Boston Magazine even named Onesimus one of the 100 best Bostonians of all time.

Nolen, the first Black woman to serve as Student Council President at Harvard Medical School, is one of those experts contributing to that work by writing essays and opinion pieces about Onesimus. She said she hoped spreading his story helps modern audiences understand the privilege of those who had the tools to write history. 

Billie Weiss | Boston Red Sox | Getty Images
A guest receives the Pfizer vaccine as the ballpark is opened as a COVID-19 Coronavirus pandemic public vaccination site on January 29, 2021 at Fenway Park in Boston, Massachusetts.

Nolen said the same discrimination that Onesimus faced still happens today in medicine, causing more distrust among Black Americans when it comes to receiving the COVID-19 vaccine. 

“We see how a lot of Black folks are less willing to just go and get the vaccine compared to some other communities. It's because of that same exact history of oppression and slavery,” she said. “All of those things still continue to play out in today's society, whether that's through different health outcomes that we see in maternal mortality or the way that COVID-19 has disproportionately impacted Black communities.” 

Learning Onesimus's story, Nolen said, can help counter that mistrust of vaccinations.

"If we knew more of the whole history and traced that back, we see that Black folks have played such a huge role in vaccinations," she said. "And it's something that we should be deeply proud of, and I think Onesimus is a major part of that story."

There are historical reasons why Black people distrust the health care system, but implicit bias in how Black patients are treated also plays a role. A Massachusetts school is doing something about it.
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