History of smallpox

The history of smallpox extends into pre-history.^[1] Genetic evidence suggests that the smallpox virus emerged 3,000 to 4,000 years ago.^[2] Prior to that, similar ancestral viruses circulated, but possibly only in other mammals, and possibly with different symptoms. Only a few written reports dating from about 500 AD to 1000 AD are considered reliable historical descriptions of smallpox, so understanding of the disease prior to that has relied on genetics and archaeology. However, during the 2nd millennium AD, especially starting in the 16th century, reliable written reports become more common.^[2] The earliest physical evidence of smallpox is found in the Egyptian mummies of people who died some 3,000 years ago.^[3] Smallpox has had a major impact on world history, not least because indigenous populations of regions where smallpox was non-native, such as the Americas and Australia, were rapidly and greatly reduced by smallpox (along with other introduced diseases) during periods of initial foreign contact, which helped pave the way for conquest and colonization. During the 18th century, the disease killed an estimated 400,000 Europeans each year, including five reigning monarchs, and was responsible for a third of all blindness.^[4] Between 20 and 60% of all those infected—and over 80% of infected children—died from the disease.^[5]

During the 20th century, it is estimated that smallpox was responsible for 300–500 million deaths.^[6][7][8] In the early 1950s, an estimated 50 million cases of smallpox occurred in the world each year.^[9] As recently as 1967, the World Health Organization estimated that 15 million people contracted the disease and that two million died in that year.^[9] After successful vaccination campaigns throughout the 19th and 20th centuries, the WHO certified the global eradication of smallpox in May 1980.^[9] Smallpox is one of two infectious diseases to have been eradicated, the other being rinderpest, which was declared eradicated in 2011.^[10][11][12]