On this day March 4, 1918

The first case of Spanish flu occurs, the start of a devastating worldwide pandemic.

It was caused by an unusually severe and deadly Influenza A virus strain of subtype H1N1. Historical and epidemiologic data are inadequate to identify the geographic origin of the virus.

Most of its victims were healthy young adults, in contrast to most influenza outbreaks which predominantly affect juvenile, elderly, or otherwise weakened patients.

The pandemic lasted from March 1918 to June 1920, spreading even to the Arctic and remote Pacific islands. It is estimated that anywhere from 20 to 100 million people were killed worldwide, or the approximate equivalent of one third of the population of Europe, more than double the number killed in World War I.

This extraordinary toll resulted from the extremely high illness rate of up to 50% and the extreme severity of the symptoms, suspected to be caused by cytokine storms.

The disease was first observed at Fort Riley, Kansas, United States, on March 4, 1918, and Queens, New York, on March 11, 1918. In August 1918, a more virulent strain appeared simultaneously in Brest, France, in Freetown, Sierra Leone, and in the U.S. at Boston, Massachusetts. The Allies of World War I came to call it the Spanish flu, primarily because the pandemic received greater press attention after it moved from France to Spain in November 1918. Spain was not involved in the war and had not imposed wartime censorship.

Scientists have used tissue samples from frozen victims to reproduce the virus for study. Given the strain’s extreme virulence there has been controversy regarding the wisdom of such research.

Among the conclusions of this research is that the virus kills via a cytokine storm, which explains its unusually severe nature and the unusual age profile of its victims (the virus caused an overreaction of the body’s immune system—the strong immune systems of young adults ravaged the body, while the weaker immune systems of children and middle-aged adults caused fewer deaths).

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