Collapse · 1918–1920

The 1918 influenza pandemic

Haskell County, Kansas (earliest probable recorded cases)

An H1N1 influenza virus caused an exceptionally deadly pandemic at the end of World War I and after; the earliest probable cases were documented in Haskell County, Kansas, in March 1918, though the virus's geographic origin is still uncertain. In two years an estimated 500 million people, nearly a third of the world's population, were infected, and estimates of deaths range from 17 million to 50 million, possibly as high as 100 million, with unusually high mortality among young adults.

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