1918 Flu W Shaped

About 1918 Flu W Shaped

A distinctive feature of the 1918 Spanish Flu was the W shaped mortality curve. Typical influenza pandemics produce a U shaped curve with high mortality in the very young and very old. The 1918 pandemic added a third peak of mortality in young adults aged 20 to 40. This age group typically has the lowest influenza mortality. The W shaped curve was observed globally, suggesting a consistent biological mechanism. One prominent hypothesis is cytokine storm, where the robust immune systems of young adults mounted an excessive inflammatory response to the novel virus. Older adults may have had some protection from prior exposure to similar H1N1 like viruses circulating before 1889. The high mortality in pregnant women was particularly devastating. The W shaped curve made the 1918 pandemic uniquely terrifying, as it killed the healthiest segment of the population. Understanding this mechanism informs pandemic preparedness planning.