On December 9, 1979, a commission of scientists declare smallpox has been eradicated. The disease, which carries around a 30 percent chance of death for those who contract it, is the only infectious disease afflicting humans that has officially been eradicated.

Something similar to smallpox had ravaged humanity for thousands of years, with the earliest known description appearing in Indian accounts from the 2nd century BCE. It was believed that the Egyptian Pharaoh Ramses V died of smallpox in 1145 BCE; however, recent research indicates that the actual smallpox virus may have evolved as late as 1580 CE. A type of inoculation—introducing a small amount of the disease in order to bring on a mild case that results in immunity—was widespread in China by the 16th century.

There is no record of a smallpox-like illness in the Americas before European contact, and the fact that Europeans brought pox with them was a major factor in their conquest and near-eradication of many of the indigenous peoples of North, South and Central America. Smallpox was the leading cause of death in 18th century Europe, leading to many experiments with inoculation. In 1796 the English scientist Edward Jenner discovered a vaccine. Unlike other types of inoculation, Jenner’s vaccine, made from a closely-related disease that affects cows, carried zero risk of transmission.

Many European countries and American states made the vaccination of infants mandatory, and incidents of smallpox declined over the 19th and early 20th centuries. Compared to other epidemic diseases, such as polio or malaria, smallpox eradication was relatively simple because the disease lives only in humans, making human vaccination highly effective at stopping its spread, and its symptoms appear quickly, making it easy to identify and isolate outbreaks.

Starting in 1967, the World Health Organization undertook a worldwide effort to identify and stamp out the last remaining outbreaks of the disease. By the mid-'70s, smallpox was only present in the Horn of Africa and parts of the Indian subcontinent. The last naturally occurring case was diagnosed in Somalia in 1977. Two years later, doctors proclaimed its eradication. The elimination of smallpox is one of the major successes in the history of science and medicine.