Edward Jenner – The Story of How He Discovered the Smallpox Vaccine through Observation and a Remarkable Experiment

In the Western world today, we can hardly imagine how devastating the infectious smallpox virus was in the past. Lots of children died of smallpox, which could also wipe out a significant part of the whole population – especially in cities because there it could spread more quickly and easily. It is (/ was) estimated, for example, that this terrible disease led to the death of a fourth of England’s population during the 17th century.

The symptoms include high fever, pain and a skin eruption. Accordingly, the skin is then covered with fluid filled blisters. But in 1980 the World Health Organisation announced the global eradication of smallpox by stating: “Smallpox is dead.” Nowadays, the few remaining specimens of this dangerous virus are kept by just two laboratories in the U.S.A. and in Russia.

The foundation for the eradication of the smallpox virus was laid by the English country doctor Edward Jenner (1749-1823). He practiced at his hometown Berkeley, Gloucestershire. Towards the end of the 18th century, he discovered the smallpox vaccine through his observations and a ‘remarkable’ – but from today’s perspective disputable – experiment.

Our story begins in 18th-century rural Gloucestershire. Besides Jenner, ‘the hero of the story’, the protagonists were milkmaids, cows and an eight-year-old boy.

Jenner’s Observant Eye – Milkmaids Provided the First Clue

It was known in rural Gloucestershire that milkmaids contracted cowpox, a relatively mild viral infection, because of their work with cows. Although they had blisters on their hands, the milkmaids seemed to have become more resistent to the serious smallpox virus. Hence, the milkmaids in Gloucestershire provided the first clue.

Edward Jenner noticed this with his, so to speak, ‘observant eye’ and made further observations of milkmaids over some years. Eventually, he developed the hypothesis that    inoculation with cowpox could potentially immunize against smallpox. However, to test whether material from cowpox blisters could protect against smallpox, he had to perform an experiment.

The Experiment with a Young Boy

The practice of inoculation was common in England. After Lady Mary Wortley Montagu (1689-1762) had witnessed the effectiveness of inoculation in Constantinople, she had her young son and, later in England, her daughter inoculated. She also convinced Caroline, the Princess of Wales, to try the treatment on her daughters in 1721. Note that the procedure had previously been tested on criminals, who were sentenced to death. They survived and were afterwards released from prison.

During the 18th century a German named Jobst Bose, the English farmer Benjamin Jesty (1736-1816) and a few others had arguably injected material from cowpox into some individuals as a means of protection against smallpox before Jenner started his experiments. Nevertheless, the latter conducted the decisive experiment in 1796.

First of all, Jenner removed some of the pus from a cowpox lesion he found on the hand of Sarah Nelmes, an infected milkmaid. Subsequently, he rubbed this pus into cuts or scratches in the skin of the arms of an eight-year-old boy. His name was James Phipps, the son of his gardener.

The young boy remained relatively well, even though he suffered from mild discomfort (i.e. a day’s fever). Six weeks later, the country doctor injected the young boy with ordinary smallpox material. Despite this exposure to smallpox material, James Phipps was unaffected and survived. Since the boy was immune, Jenner confirmed the effectiveness of this kind of inoculation or – what we nowadays call ‘vaccination’ – with the help of his novel approach.

From our today’s point of view, Jenner’s experiment certainly seems disconcerting. Such an experiment with an eight-year-old boy would surely have been forbidden by a medical ethics committee. Unsurprisingly, already in his own lifetime, his approach prompted some initial negative reactions.

From a Cartoon of People with Cows‘ Heads and Other Negative Reactions to Compulsory ‘Vaccination’

The Royal Society rejected the publication of Jenner’s original paper. Edward Jenner thus set about publishing his account An Inquiry into the Cause and Effects of Variolae Vaccinae, or Cowpox (1798) privately. It should be noted that the beginning of the word “Vaccinae” refers to the Latin word for cow, “vacca.” Therefore, the term vaccination has come into use.

Initially, some people were, of course, suspicious of the new technique of vaccination and reacted negatively. For instance, one complaint related to the alleged ‘contamination’  of humans with matter from a cowpox lesion or, in general, with animal material. There was also a cartoon that depicts a vaccine institution, in which cows‘ heads and hooves grow out of vaccinated people’s body parts.

Yet, the idea of vaccination slowly became popular in Britain and abroad. Interestingly, an Act of Parliament made vaccination compulsory.

As for Jenner, he acquired hero status. He received grants from the British Parliament and was praised by, among others, the famous U.S. Founding Father Thomas Jefferson and Napoleon.


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Stevenson, Leslie, and Henry Byerly. The Many Faces of Science: An Introduction to Scientists, Values, and Society. Boulder (et al.): Westview Press, 1995.