Smallpox was one of the deadliest diseases in human history, killing hundreds of millions of people over thousands of years. In 1980 the World Health Organization declared it eradicated, wiped from the face of the Earth by a worldwide vaccination campaign. It remains the only human disease ever to have been deliberately eliminated, a singular triumph of medicine and one of the clearest demonstrations that vaccination works.
For most of recorded history smallpox was a constant terror. It killed roughly a third of those it infected, left many survivors blind or deeply scarred, and shaped the course of empires and populations. As recently as the twentieth century it was still killing millions of people every year. There was no cure, and the only defence was to prevent infection in the first place.
The path to eradication began in 1796, when the English doctor Edward Jenner showed that infecting a person with the mild cowpox virus protected them against smallpox. This was the first vaccine, and the very word vaccine comes from the Latin for cow. Over the following two centuries the evidence became overwhelming: wherever vaccination was widely used, smallpox retreated and disappeared. The protection it gave was real, repeatable, and beyond dispute.
In 1967 the World Health Organization launched an intensified worldwide effort, tracking down every outbreak and vaccinating everyone around each case to cut off the chains of transmission. Country by country the disease was cornered. The last natural case of the most severe form was recorded in Bangladesh in 1975, and the final natural case of any smallpox occurred in Somalia in 1977. After years of careful checking, the disease was declared eradicated in 1980.
The conquest of smallpox stands almost alone in the history of medicine. Only one other disease, the cattle plague rinderpest, has since been eradicated, and no other human disease has yet followed smallpox into oblivion, though efforts continue against polio and others. The virus now survives only in a small number of secure laboratories.
The eradication of smallpox is more than a historical milestone. It is a vast, planet wide demonstration, carried out on the whole human species, that vaccination can prevent disease so completely that the disease itself ceases to exist. Few facts in medicine are established on such a scale or with such finality.
