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In response to the growing spread of monkeypox, public health leaders are for the first time since the 1970s opening the locked stockpiles of smallpox vaccines to control the spread of the virus. But here’s something to consider: Those vaccines originated as a direct result of slavery.

The history of people becoming sick and dying from epidemics is timeless. But the practice of vaccinating people to prevent the spread of infectious disease is a relatively new phenomenon in the U.S. and Europe. The first vaccine in the U.S. was introduced by an enslaved African named Onesimus in 1721. To prevent the spread of smallpox in colonial Boston, Zabdiel Boylston, a doctor, followed Onesimus’ instructions and took the lymph, the colorless fluid within a smallpox vesicle, and injected it into the arm of his son and two enslaved people in his home.


This process, known as variolation, infects a susceptible person with the smallpox virus in hopes of their developing a milder version and surviving. In 18th-century Boston, people considered it superstitious and scary. Many initially refused to get vaccinated, but Boylston experimented on other enslaved people and used their results to illustrate the effectiveness of the procedure.

One legacy of this work is that the practice of vaccination in the U.S. cannot be divorced from the history of slavery.

Smallpox vaccination required experimentation on human bodies to provide evidence that it worked. European empires turned to oppressed populations to advance medical science. When smallpox spread throughout the Spanish Empire in the Caribbean and South America, King Carlos IV launched the first global immunization campaign in 1803. At the time, medical officials typically transported smallpox vaccine by placing it between two pieces of glass, but the treacherous voyage across the temperamental Atlantic Ocean made that impossible. According to physician-historian José G. Rigau-Pérez, Spanish officials purposely infected orphans with the virus so that their bodies would incubate it. As a part of a royal expedition, 22 orphans were split into pairs, and every nine or 10 days another pair was infected with the virus to produce the vaccine matter. In essence, the orphans became vaccine mules.


As medical officials in Puerto Rico waited for the royal expedition to arrive, the smallpox epidemic exploded across the Caribbean. Government officials forcibly removed infected family members from their homes to be placed in quarantine on a remote part of the island. Francisco Oller, chief surgeon of the Royal Military Hospital, had learned that English physician Edward Jenner discovered that cowpox could be used as a vaccine matter, and that a doctor in St. Thomas had been using it as a defense against the spread of the virus. The doctor sent the vaccine matter between two pieces of glass to Oller, who used it to vaccinate his two sons. One of his sons contracted the virus and later produced the lymph that was used to vaccinate others on the island.

Having witnessed the lymph on the boy’s body, the governor of Puerto Rico then called for a vast public vaccination to be administered throughout San Juan, the capital city. The governor, in turn, requested more lymph from officials in St. Thomas, who sent it not only on glass but also, according to Rigau-Pérez, “on the arm of a recently vaccinated infant slave girl” to make sure the vaccine arrived safely.

When smallpox resurfaced in the United States during the Civil War, both Union and Confederate armies lacked vaccine material to protect soldiers. Army medical officials on both sides infected enslaved infants and newly emancipated children with smallpox and harvested vaccine matter off their bodies.

Confederate doctor James Bolton traveled throughout Virginia infecting enslaved people with smallpox with the hope that their bodies would produce the lymph that could be used as a vaccine matter. After the patients developed a mild version of smallpox and began to recover, Bolton “retraced his steps for the purpose of gathering the crusts.” According to a surviving report, “the result of the expedition was about eight hundred crusts, mostly from healthy negro children.” Similarly, in Benton Barracks, Mo., a Northern physician infected a group of formerly enslaved children within a refugee camp with the virus to harvest lymph for vaccinating Union soldiers.

Evidence of using enslaved populations to harvest vaccine matter does not appear in boldface headlines in 19th-century medical journals, nor is it easily discoverable by doing keyword searches in online archives. Documenting how slavery contributed to the world did not matter to many of these medical and political officials. They were more invested in figuring out what works — but in the process, they unwittingly recorded their own violations and inhumane practices.

The modern world depends on vaccinations for a range of maladies, distributing them eagerly and praising their effectiveness, without acknowledging that the beginning of these medical interventions can be traced to slavery. It is no coincidence that the practice of artificially triggering the immune system to create antibodies developed at the same time when millions of people were held in bondage and had little to no say in what was done to their own bodies.

Jim Downs is a historian and professor of Civil War studies at Gettysburg College in Gettysburg, Penn., and author of “Maladies of Empire: How Colonialism, Slavery, and War Transformed Medicine” (Harvard University Press, 2021).

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