Edward Jenner, an English doctor, is widely credited as the inventor of the modern vaccine. In May 1796, he took material from a cowpox sore on the hand of a dairymaid named Sarah Nelms and injected it into an eight-year-old boy named James Phipps, demonstrating that exposure to a milder disease could protect against the deadly smallpox virus. But the full story is longer and more interesting than one man’s experiment. The idea of training the body to fight disease stretches back thousands of years, and the vaccines we use today are the product of dozens of breakthroughs by scientists across centuries.
Variolation: The Idea Before the Invention
Long before Jenner, people in Asia and parts of Africa practiced something called variolation: deliberately exposing healthy people to small amounts of material from smallpox sores. The resulting illness was usually milder than a natural infection, and far less likely to kill. Some sources suggest this practice dates back as far as 200 BCE.
Written records from the mid-1500s describe a Chinese technique called insufflation, in which dried smallpox scabs were ground into powder and blown into a person’s nostril through a pipe. The practice was effective enough that it spread across trade routes and eventually reached the Ottoman Empire, where it caught the attention of Lady Mary Wortley Montagu, wife of the British ambassador to Turkey. In 1721, she introduced variolation to England after witnessing it firsthand in Istanbul. Her advocacy helped the practice gain a foothold in European medicine, setting the stage for what came next.
Edward Jenner and the First Vaccine
Jenner was a country doctor in Gloucestershire who noticed that milkmaids who had contracted cowpox, a relatively mild disease, seemed to be immune to smallpox. He tested this observation in 1796 by inoculating young James Phipps with cowpox material, then later exposing the boy to smallpox. Phipps didn’t get sick. Jenner published his findings, and the technique spread rapidly across Europe and beyond.
The word “vaccine” itself comes from Jenner’s work. It derives from “vaccinia,” the scientific name for the cowpox virus, which in turn comes from the Latin word “vacca,” meaning cow. What made Jenner’s approach different from variolation was the key insight: you could use a related but less dangerous virus to build protection, rather than risking exposure to the disease itself. That principle still underpins much of vaccine design today. Jenner’s vaccine eventually led to one of medicine’s greatest achievements: the World Health Organization certified the global eradication of smallpox in December 1979, making it the first human disease ever wiped out entirely.
Pasteur Turns Vaccines Into a Science
For nearly a century after Jenner, vaccination remained limited to smallpox. That changed with Louis Pasteur, the French chemist and microbiologist who proved that vaccines could be deliberately designed in a laboratory. Pasteur showed that weakening a pathogen through various lab techniques could strip away its ability to cause serious disease while still training the immune system to recognize it.
His most dramatic demonstration came on July 6, 1885, when he injected the first of 14 daily doses of progressively weakened rabies virus into nine-year-old Joseph Meister, who had been severely bitten by a rabid dog two days earlier. The boy survived. Pasteur had proven that laboratory-crafted vaccines could protect against diseases beyond smallpox, and that they could work even after exposure. His approach of weakening or inactivating pathogens became the foundation for vaccine development well into the 20th century.
Maurice Hilleman: The Most Prolific Vaccine Maker
If Jenner invented the concept and Pasteur built the science, Maurice Hilleman industrialized it. Working primarily at Merck from the 1950s through the 1990s, Hilleman and his colleagues developed more than 40 experimental and licensed vaccines for humans and animals. Of the 14 vaccines routinely recommended in the United States, Hilleman created eight of them.
His list of contributions is staggering: measles (1963), mumps (1967), rubella (1969), hepatitis A, hepatitis B, chickenpox, pneumonia, meningitis, and pandemic influenza, among others. He also developed a vaccine for Japanese encephalitis as early as 1944. Despite saving more lives than perhaps any other scientist of the 20th century, Hilleman remains largely unknown outside the medical world.
The Polio Vaccines That Changed Public Health
Few diseases terrified mid-century Americans more than polio, which could paralyze or kill children seemingly at random. Jonas Salk, working at the University of Pittsburgh with funding from the National Foundation for Infantile Paralysis (now the March of Dimes), developed an inactivated polio vaccine using killed virus. On April 12, 1955, a massive field trial led by Thomas Francis Jr. at the University of Michigan confirmed that it worked. The announcement was met with national celebration.
Six years later, in 1961, Albert Sabin’s oral polio vaccine was licensed. Unlike Salk’s injected version, Sabin’s vaccine used a weakened live virus and could be given as drops in the mouth, making it easier to distribute in low-resource settings. The oral vaccine became the primary tool in the global campaign to eradicate polio, which has brought the disease to the brink of elimination worldwide.
Genetic Vaccines and the mRNA Breakthrough
The next major leap in vaccine technology came from genetic engineering. In 1986, the first vaccine produced using recombinant DNA technology was approved for hepatitis B. Rather than growing the actual virus, researchers led by William Rutter and Pablo Valenzuela engineered yeast cells to produce a single viral protein that could trigger an immune response. This approach was safer and easier to manufacture at scale, and it opened the door to designing vaccines at the molecular level.
That door eventually led to mRNA vaccines, which made headlines during the COVID-19 pandemic but were the product of more than 50 years of research. Scientists first discovered mRNA and its role in protein production between 1961 and 1990. A key breakthrough came in 2005, when researchers showed that chemically modified mRNA could deliver instructions to cells without triggering a dangerous overreaction from the immune system. Over the following decade, scientists at the NIH and elsewhere figured out how to wrap mRNA in tiny fat particles called lipid nanoparticles to deliver it into cells, and how to stabilize the “spike proteins” that coronaviruses use to invade cells.
By 2016, NIH scientists and the biotech company Moderna had begun collaborating on a general mRNA vaccine design that could be quickly adapted to new viruses. When COVID-19 emerged in late 2019, that groundwork allowed mRNA vaccines to move from concept to clinical use in under a year. The speed was unprecedented, but the science behind it had been building for decades.
No Single Inventor
The honest answer to “who invented vaccines” is that no single person did. Jenner gets the credit, and deservedly so, for demonstrating the principle in a way that could be tested, repeated, and scaled. But he built on centuries of folk medicine from China, Africa, and the Ottoman Empire. Pasteur expanded the idea beyond one disease. Hilleman turned it into a mass production effort that reshaped childhood health. Salk and Sabin tackled polio from two different angles. And generations of molecular biologists made it possible to design vaccines from genetic code rather than whole viruses. Vaccination is less a single invention than a chain of discoveries, each one unlocking the next.