Approximately 675,000 Americans died from the Spanish flu, which struck in three waves between March 1918 and the summer of 1919. At the time, the U.S. population was roughly 103 million, meaning the pandemic killed about 1 in every 150 people in the country. Globally, the virus claimed at least 50 million lives.
Why the True Number May Be Higher
The 675,000 figure is an estimate, and likely a conservative one. In 1918, the U.S. Census Bureau’s death registration system covered only about 78% of the population. Rural areas, Indigenous communities, and much of the South had limited or no systematic death reporting. The Census Bureau itself estimated that 445,000 deaths occurred in the last four months of 1918 alone, but only about 346,000 of those fell within the registration area where records were actually kept. The remaining deaths had to be extrapolated. Many flu deaths were also recorded as pneumonia or other complications, further muddying the count.
Three Waves, One Devastating Fall
The pandemic arrived in three distinct phases. The first wave appeared in March 1918, when more than 100 cases were reported at Camp Funston in Fort Riley, Kansas. This spring wave was relatively mild.
The second wave, in the fall of 1918, was catastrophic. It accounted for the majority of all U.S. deaths attributed to the pandemic. The virus had mutated into a far more lethal form, and it swept through military camps, cities, and towns with devastating speed. A third wave followed during the winter and spring of 1919, adding to the death toll before the pandemic finally subsided that summer.
Who Died: The Unusual Age Pattern
Most flu pandemics kill the very young and the very old, producing a U-shaped mortality curve. The 1918 pandemic was different. It added a third peak: adults between 20 and 40 years old died at shockingly high rates, creating what epidemiologists call a W-shaped curve. Healthy young adults, the group normally most resilient to influenza, were among the hardest hit.
The leading explanation involves the body’s own immune response. In severe cases, the immune system flooded the lungs with inflammatory proteins in excessive quantities, causing dangerous fluid buildup that made the illness worse rather than better. A strong, vigorous immune system, exactly the kind a healthy 25-year-old would have, could paradoxically become the thing that killed them. This overreaction was compounded by bacterial pneumonia, which was the most common direct cause of death. Antibiotics did not yet exist.
The Military Toll
The pandemic hit U.S. military forces especially hard. About 45,000 American soldiers died of influenza and related pneumonia by the end of 1918, nearly matching the 53,402 American combat deaths in all of World War I. Crowded training camps and troop ships created ideal conditions for the virus to spread. The first wave was actually detected at a military installation, and the movement of soldiers across the Atlantic helped carry the virus worldwide.
Cities That Acted Early Fared Better
The pandemic’s toll varied dramatically from city to city, and timing was the key variable. Cities that introduced public health measures within days of their first reported cases, closing schools, banning public gatherings, enforcing quarantines, achieved significant reductions in both peak and overall mortality. Cities that waited, or that relaxed restrictions too early, paid a steep price. A study of 17 U.S. cities found that places implementing measures promptly and sustaining them throughout the threat experienced roughly 50% lower excess death rates on average.
St. Louis, which acted relatively quickly, recorded an excess death rate of 325 per 100,000 during the fall wave. Cleveland, slower to respond, suffered a rate of 414 per 100,000. Philadelphia, which infamously held a massive public parade in September 1918 despite warnings, became one of the hardest-hit cities in the country.
Economic Disruption and a Labor Shortage
Because the virus disproportionately killed working-age men between 18 and 40, the economic consequences were severe. Coal mines reported a 50% decrease in production. In Memphis, nearly a third of the street railway’s workforce was incapacitated at one point. Factories that were already short-staffed from the military draft lost even more workers to illness and death.
The mass loss of prime-age workers left many families without their primary breadwinner. For the labor market as a whole, the shortage pushed wages upward. Cities and states with higher flu mortality experienced greater manufacturing wage growth between 1914 and 1919, a grim economic silver lining driven by the simple fact that surviving workers were suddenly in high demand.
The Impact on Life Expectancy
The 1918 pandemic caused the single largest one-year drop in U.S. life expectancy ever recorded. Life expectancy fell 11.8 years in 1918 alone, the culmination of a three-year decline from 1915 to 1918 that totaled 15.4 years. No other event in the history of U.S. vital statistics, not a war, not another epidemic, produced a comparable collapse.
Comparison to COVID-19
COVID-19 eventually surpassed the 1918 pandemic in raw U.S. deaths, with total American fatalities exceeding one million by early 2022. But context matters. The U.S. population in 2020 was more than three times larger than in 1918, so the 1918 flu killed a far greater share of the population. The 1918 virus also compressed most of its lethality into roughly six months during the fall and winter waves, while COVID-19 deaths accumulated over several years. Both pandemics reshaped public health policy, but the 1918 flu did so in an era without antiviral drugs, mechanical ventilators, or any real understanding of how viruses worked.