It killed more people in a year than World War I killed in four.

The Spanish Flu: History's Deadliest Pandemic

A mysterious illness kills 50 million people in 18 months

The 1918 Spanish flu pandemic killed 50-100 million people in 18 months — more than World War I — and transformed global public health forever.

In March 1918, soldiers at Camp Funston, Kansas reported symptoms of a severe influenza — fever, cough, and fatigue. The first wave was relatively mild. The second wave, which emerged in the fall of 1918, was catastrophically deadly. Young adults, who typically fare best in flu epidemics, were dying at unprecedented rates.

The 1918 influenza pandemic — wrongly called the "Spanish flu" because neutral Spain's uncensored press reported it freely while Allied and Central Powers countries suppressed the news to maintain wartime morale — killed an estimated 50 to 100 million people worldwide. This was more than died in World War I. With global population at 1.8 billion, it killed between 3% and 6% of humanity.

The virus' unusual lethality among young adults resulted from a "cytokine storm" — the immune system's overreaction that turns the body's defenses against the lungs. Healthy young people with robust immune systems were paradoxically most at risk. Victims could be healthy in the morning and dead by nightfall.

The pandemic transformed medicine and public health. It demonstrated the need for global disease surveillance, accelerated vaccine research, and led to the establishment of…

💡 In Philadelphia, the pandemic killed so many people so fast that the city ran out of coffins. Bodies were stored in churches and warehouses.