The first vaccine was created in 1796 by Edward Jenner, an English doctor who used material from cowpox blisters to protect against smallpox. But the story of immunization stretches back centuries before Jenner, and his famous experiment built on folk knowledge that had circulated among farmers and milkmaids for generations.
Smallpox: The Disease That Sparked It All
To understand why the first vaccine targeted smallpox, you need to understand how devastating the disease was. Smallpox killed roughly 30% of the people who caught it, and survivors were often left blind or severely scarred. In 18th-century England, smallpox accounted for about 5% of all deaths in the south and 10% in the north. It struck rich and poor alike, and no reliable treatment existed. The sheer terror of the disease drove people to try increasingly creative ways to prevent it.
Variolation: The Risky Predecessor
Long before Jenner, people in Asia had developed a technique called variolation: deliberately infecting someone with smallpox material to trigger a mild case and, ideally, lifelong protection. Practitioners would grind dried smallpox scabs into powder and blow it into a person’s nose. The recipient would develop a less severe form of the disease. It worked surprisingly well. Between 1% and 2% of people who were variolated died, compared to 30% who caught smallpox naturally. Those odds were grim by modern standards, but in a world ravaged by the disease, they were a gamble many were willing to take.
By 1700, variolation had spread across Africa, India, and the Ottoman Empire. Europeans learned about it through two key figures in 1721. Lady Mary Wortley Montagu, the wife of the British ambassador to Constantinople, observed the practice in Turkey and championed it back in England. At her urging, along with support from the Princess of Wales, several prisoners and abandoned children were inoculated through punctures in the skin. That same year in Massachusetts, a minister named Cotton Mather learned about the technique from an enslaved man named Onesimus, who described how it was practiced in Africa. Mather promoted it during a smallpox outbreak in Boston.
Variolation represented a genuine leap in medical thinking. But it carried a real risk of death, and people who were variolated could spread full-blown smallpox to others. The world needed something safer.
Jenner’s Experiment in 1796
Edward Jenner was a country doctor in Gloucestershire, England, and he was familiar with a piece of rural folklore: milkmaids who had caught cowpox, a relatively mild disease picked up from infected cows, seemed to never get smallpox. A farmer named Benjamin Jesty had actually tested this idea on his own family in 1774, vaccinating his wife and two sons with cowpox material taken from lesions on a cow’s udder during a smallpox epidemic. Jesty’s experiment worked, but he never published his findings or pursued the idea scientifically. He remains a largely forgotten figure in vaccine history.
Jenner took the concept further. In 1796, he collected material from a cowpox blister on a milkmaid’s hand and inoculated an 8-year-old boy named James Phipps. Several weeks later, Jenner deliberately exposed Phipps to smallpox. The boy didn’t get sick. Cowpox had made him immune.
The reason this worked is that cowpox and smallpox are closely related viruses. They share enough surface proteins that the immune system, after fighting off cowpox, recognizes and attacks smallpox before it can take hold. Cowpox itself caused only mild symptoms in humans, making it far safer than variolation with actual smallpox material.
The Ethics Were Troubling
By today’s standards, Jenner’s experiment raises serious ethical concerns. James Phipps was 8 years old and could not consent to what was being done to him. We don’t know whether his parents fully understood the risks. Jenner had no real understanding of how much protection cowpox would provide, and if it hadn’t worked, exposing Phipps to smallpox could have killed him. His entire hypothesis rested on folk observation, not controlled testing. Modern vaccine trials require extensive preliminary research, informed consent from competent adults, and rigorous safety assessment before anyone is deliberately exposed to a pathogen.
Why It’s Called a “Vaccine”
The word vaccine comes directly from Jenner’s use of cowpox. The Latin word for cow is “vacca,” and the cowpox virus is formally called vaccinia. For nearly a century after Jenner, the terms “vaccine” and “vaccination” referred specifically to the cowpox procedure for preventing smallpox.
That changed in 1885, when Louis Pasteur in Paris developed a rabies treatment. On July 6 of that year, Pasteur injected the first of 14 daily doses of progressively weakened rabies virus into a 9-year-old boy named Joseph Meister, who had been severely bitten by a rabid dog two days earlier. The boy survived. Pasteur deliberately called his creation a “rabies vaccine,” borrowing Jenner’s terminology even though it had nothing to do with cows or cowpox. The move was partly an homage and partly strategic branding. It worked. From that point on, “vaccine” expanded to mean any preparation that trains the immune system against a specific disease.
Pasteur’s contribution was also a turning point in method. Jenner had relied on a natural observation, harvesting material from cowpox blisters found on animals. Pasteur created his vaccine in a laboratory, deliberately weakening a virus through controlled techniques. He proved that scientists could systematically modify pathogens to make them safe enough to use as vaccines. The CDC has described his work as “the beginning of the modern era of immunization.”
From First Vaccine to Eradication
Jenner’s smallpox vaccine launched nearly two centuries of increasingly organized vaccination campaigns. Countries began mandating smallpox vaccination in the 1800s, and by the 20th century, the World Health Organization coordinated a global eradication effort. The last naturally occurring case of smallpox was recorded in 1977. On December 9, 1979, a global commission certified that smallpox had been eradicated, and the 33rd World Health Assembly made it official on May 8, 1980, declaring: “The world and all its peoples have won freedom from smallpox.”
Smallpox remains the only human disease ever fully eradicated. Routine vaccination was discontinued after 1980 because the disease no longer existed in the wild, and the vaccine itself carried a small risk of serious side effects, particularly for people with weakened immune systems. The entire arc, from Jenner’s experiment on a single child to a disease eliminated from the planet, took 184 years.