Edward Jenner

On May 14, 1796, an English country physician named Edward Jenner took material from a cowpox blister on the hand of a milkmaid named Sarah Nelmes and inoculated it into the arm of an eight-year-old boy named James Phipps. Six weeks later, Jenner exposed the boy to smallpox. James Phipps did not develop the disease. It was the first deliberate vaccination in history — a word that Jenner himself would coin, from vacca, the Latin for cow — and it set in motion a process that would, 184 years later, result in the complete eradication of smallpox from the face of the Earth. No human disease has ever been eradicated before or since.

Edward Jenner was born on May 17, 1749, in Berkeley, Gloucestershire, England, the eighth of nine children of a Church of England vicar. His father died when he was five, and he was sent to live with an elder brother. He was apprenticed to a surgeon at thirteen and moved to London at twenty-one to study under the great anatomist John Hunter, a relationship that proved formative. Hunter was a meticulous experimentalist who insisted on empirical evidence over theory; his famous advice to Jenner — "Don't think, try" — seems prescient in retrospect. Jenner returned to Berkeley in 1773 to practice as a country physician and never left.

Smallpox was one of the most feared diseases in human history. In the eighteenth century it killed an estimated 400,000 Europeans annually, and left many more blind, scarred, or otherwise disabled. The practice of variolation — deliberately inoculating people with material from smallpox pustules to induce a milder protective infection — had been introduced to Britain from the Ottoman Empire in the 1720s and was practiced, though imperfectly and sometimes fatally. Jenner had been variolated himself as a boy and had observed something that country physicians had long noted informally: milkmaids who contracted cowpox, a mild disease of cattle that occasionally passed to humans, seemed to be protected from smallpox thereafter. The observation was folk knowledge. Jenner decided to test it scientifically.

The key insight — and it was a profound one — was not simply that cowpox conferred protection, but that it could be transferred from person to person through deliberate inoculation while remaining mild and safe. This made it a practical preventive measure on a population scale. Variolation with actual smallpox carried real risk of severe disease and transmission. Vaccination with cowpox material carried neither. Jenner conducted further experiments, vaccinated more subjects, and in 1798 published his findings in a pamphlet: An Inquiry into the Causes and Effects of the Variolae Vaccinae. The reception was initially skeptical — one critic suggested the vaccine might cause people to grow bovine features — but the evidence accumulated rapidly.

Within years, vaccination was spreading across Europe and the Americas. Napoleon, though at war with Britain, had all his troops vaccinated and reportedly called Jenner "one of the greatest men in history." Thomas Jefferson received the vaccine and organized vaccination programs in the United States. By 1801, Jenner estimated that 100,000 people in Britain alone had been vaccinated. The British government awarded him £10,000 in 1802 and a further £20,000 in 1807. The Royal Jennerian Society was established to promote worldwide vaccination. Jenner himself spent enormous energy and resources corresponding with physicians and governments around the world, distributing vaccine material, and championing the practice without seeking personal profit.

Jenner did not understand why vaccination worked — the germ theory of disease lay sixty years in the future with Pasteur, and the concept of the immune system did not yet exist. He observed, tested, and published; the mechanism would be explained by later generations. His method of deliberately using a mild, related pathogen to build protection against a deadly one established the principle that Pasteur would later generalize into the science of immunology. Every vaccine ever developed — against polio, measles, influenza, COVID-19 — is a direct intellectual descendant of Jenner's experiment in that Gloucestershire garden.

Jenner died on January 26, 1823, at his home in Berkeley, of a stroke, aged seventy-three. He never sought wealth from his discovery. The World Health Organization certified the global eradication of smallpox in 1980 — 157 years after his death. The last natural case had occurred in 1977. It is estimated that Jenner's discovery has saved more human lives than those of any other individual in history: well over 300 million people who would otherwise have died of smallpox in the twentieth century alone were spared by vaccination programs that began with that first inoculation of James Phipps in 1796.

Jenner Among the Pioneers of Preventive Medicine

Explore More Geniuses