The 1918 flu pandemic (commonly referred to as the Spanish flu) was a category 5 influenza pandemic that started in the United States, appeared in West Africa and France and then spread to nearly every part of the globe. It was caused by an unusually severe and deadly Influenza A virus strain of subtype H1N1. Many of its victims were healthy young adults, in contrast to most influenza outbreaks which predominantly affect juvenile, elderly, or otherwise weakened patients.
The Spanish flu pandemic came in three waves lasting from March 1918 to June 1920, spreading even to the Arctic and remote Pacific islands. While older estimates put the number of killed at 40–50 million people, current estimates are that 50 million to 100 million people worldwide died, possibly more than that taken by the Black Death, and higher than the number killed in World War I. This extraordinary toll resulted from the extremely high infection 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 West Africa at 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 - strong immune systems (ie young adults) ravaged the body, while weaker immune systems (ie children & middle age adults) caused less morbidity and mortality).
