When did the Spanish flu pandemic happen?

The Spanish flu was a devastating influenza pandemic that swept the globe from 1918 to 1920, near the end of the First World War. Caused by an especially virulent H1N1 influenza virus, it infected roughly 500 million people, about a third of the world population at the time, and killed an estimated 50 million or more, though some estimates run higher. Unusually, it caused severe illness and death in healthy young adults, not just the very young and old. Despite its name, the flu did not originate in Spain; the country simply reported it openly because, as a neutral nation in the war, it did not censor its press, while combatant countries suppressed the news. Crowded wartime conditions and troop movements helped the disease spread rapidly around the world.