From a Milkmaid's Observation to mRNA
In 1796, English physician Edward Jenner acted on a piece of local folk wisdom: milkmaids who had caught cowpox, a mild disease, seemed to be immune to smallpox, one of history's deadliest killers. Jenner tested the idea directly, taking material from a cowpox sore on a milkmaid's hand and inoculating an eight-year-old boy, James Phipps, with it. When Jenner later exposed the boy to smallpox matter, Phipps did not develop the disease. The word "vaccine" itself comes from this experiment — from the Latin vacca, meaning cow.
Nearly ninety years later, in 1885, Louis Pasteur applied a similar logic to rabies, a disease that was almost universally fatal once symptoms began. Pasteur had developed a weakened rabies vaccine tested only in animals when a mother brought him her nine-year-old son, Joseph Meister, who had been badly bitten by a rabid dog. Pasteur, not a physician, took the ethically fraught step of treating the boy with his experimental vaccine. Meister survived, and the case made Pasteur a household name across Europe.
The 20th Century's Race Against Epidemics
Polio terrified mid-century American families, paralyzing tens of thousands of children every year. In 1954, Jonas Salk's inactivated polio vaccine was tested in one of the largest clinical trials in history, involving over a million children who became known as "Polio Pioneers." The vaccine's success in 1955 was announced to a relieved nation, and Salk, who never patented his vaccine, became a household name.
Maurice Hilleman, working largely out of the public eye at Merck, developed over forty vaccines across his career, including the combined measles-mumps-rubella (MMR) vaccine in 1971 — a single shot that replaced three separate ones and dramatically simplified childhood immunization schedules. One of Hilleman's mumps vaccine strains was famously isolated from a swab taken from his own daughter's throat when she fell ill in 1963. Decades later, in 2020, the COVID-19 pandemic produced the fastest vaccine development effort in history: the Pfizer-BioNTech and Moderna vaccines were the first mRNA vaccines ever authorized for widespread human use, built on foundational research by scientists including Katalin Karikó, whose work on mRNA stability had gone largely unfunded for years before it suddenly became the center of a global public health response.
The tuberculosis vaccine, known as BCG (Bacillus Calmette-Guérin), followed a slower, more grinding path than most — French scientists Albert Calmette and Camille Guérin spent thirteen years, from 1908 to 1921, weakening a strain of bacteria across more than 200 laboratory generations before it was safe enough to use in humans. It remains one of the most widely administered vaccines in the world today, more than a century after that work began.
The clearest measure of vaccination's historical impact is smallpox: after a sustained global vaccination campaign coordinated by the World Health Organization, the disease was declared eradicated in 1980 — the only human disease ever wiped out entirely. Polio has followed a similar, nearly-complete trajectory, falling from over 350,000 annual cases worldwide in 1988 to a handful of countries today. It's also worth noting, purely as historical fact, that resistance to vaccination is nearly as old as vaccination itself — inoculation was controversial in colonial America, and organized anti-vaccination leagues existed in Victorian England within decades of Jenner's discovery.
Source: World Health Organization (WHO) and the National Library of Medicine (NIH).