On 26 October 1977, a hospital worker named Ali Maow Maalin walked into a health clinic in the Merca District of Somalia with what would become the most consequential case of smallpox in human history. He had no idea that his diagnosis marked the last naturally occurring instance of a disease that had killed hundreds of millions before him — or that his recovery would eventually be certified as one of humanity's greatest collective achievements.
The eradication of smallpox represents the only time humans have successfully eliminated an entire infectious disease from the global population. When the World Health Organization formally announced this victory on 8 May 1980, it crowned nearly two centuries of effort, beginning with Edward Jenner's pioneering vaccination in 1798 using cowpox material. What made smallpox eradicable — and what makes most diseases stubbornly resistant to eradication — comes down to biology and ingenuity working in tandem.
Smallpox came in two forms. Variola major killed up to 40 percent of those it infected; variola minor, also called alastrim, was less lethal but still devastating at less than one percent mortality. The last case of the deadlier variant struck in Bangladesh in October 1975. Then came Maalin's diagnosis two years later, the final flicker of a disease that had shaped empires and civilizations. The contacts around Maalin — all 211 of them — were traced, revaccinated, and kept under surveillance to ensure the virus had truly been cornered.
The success hinged on factors that not every disease possesses. Smallpox had no hidden animal reservoir where it could lurk and re-emerge; it lived in humans alone. An effective vaccine existed and could be mass-produced. The disease was unmistakable — no ambiguity in diagnosis. And crucially, governments and health organizations worldwide committed resources and political will to the campaign. After two years of meticulous verification, an international commission of smallpox experts certified the eradication on 9 December 1979.
Only one other disease has met this standard: rinderpest, a viral infection of cattle and other ruminants. Throughout the twentieth century, campaigns against rinderpest built momentum, particularly through live attenuated vaccines. The Food and Agriculture Organization of the United Nations led the final push, and on 14 October 2010 — after nine years without a single diagnosis — announced complete eradication.
These two victories illuminate both the possibility and the rarity of disease eradication. The Carter Center's International Task Force for Disease Eradication has identified two human diseases as current targets: dracunculiasis (Guinea worm) and lymphatic filariasis (elephantiasis). Other long-running campaigns continue against polio, yaws, hookworm, yellow fever, and malaria, each with its own biological obstacles and logistical challenges.
The smallpox story also carries a haunting coda. While the disease is gone from nature, the virus itself is preserved in laboratories in the United States and Russia. Scientists continue to debate whether these stockpiles should exist at all — the risk of accidental or deliberate release looms, particularly for populations born after vaccination programs ceased in the late 1980s. A disease we conquered remains a paradox: extinct in the world, but not quite gone from memory or from reach.