When Did the Spanish Flu Pandemic Start?

The 1918 H1N1 influenza pandemic killed an estimated 50-100 million people (3-5% of the global population), making it the deadliest pandemic in modern history. The first confirmed cases appeared at Camp Funston, a US military base in Kansas, on 4 March 1918. World War I troop movements rapidly spread the virus across continents. It was misleadingly called "Spanish flu" because wartime censorship suppressed news of the disease in combatant nations, while neutral Spain reported freely, creating the impression Spain was uniquely affected. The pandemic came in three waves: a mild first wave (spring 1918), a catastrophically lethal second wave (autumn 1918), and a third wave (winter-spring 1919). Unusually, it was most deadly among healthy 20-40-year-olds, possibly because their strong immune responses triggered fatal cytokine storms. More US soldiers died from the flu than in combat. The virus was reconstructed from preserved tissue samples in 2005, revealing it was an avian-origin H1N1 strain.