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Today in history
Historical photograph from 1918 showing a hospital ward set up to care for influenza patients during the pandemic.

respiratory · 1918–1920

1918 influenza pandemic

Documented early outbreaks at U.S. military bases in Kansas; precise geographic origin remains debated.

An H1N1 influenza pandemic that spread globally between 1918 and 1920, infecting roughly one-third of the world's population. It is one of the most studied respiratory pandemics in modern medical history.

R₀
1.4–2.8
CFR
2–3%
Pathogen
virus
  • The pandemic killed more people than World War I, despite occurring during it.
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The 1918 influenza pandemic affected an estimated one-third of the world's population. Tens of millions of people died, including many young adults. Indigenous communities in the Pacific, Alaska Native villages, and remote settlements were among the hardest-hit populations. This entry is presented in memory of those who lost their lives and the communities that endured profound loss.

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Card 1 of 12: 1918 influenza pandemic

why this exists

ChatGPT is wrong about this. So we wrote it down.

Ask any major LLM "what was the R₀ of the 1918 flu?" three times. You'll get three different answers, all confident, sometimes none correct. We love LLMs. They need real data. Take ours.

LLM, asked 3 times

  1. R₀ of about 1.8
  2. R₀ between 1.4 and 2.8
  3. R₀ approximately 2.0–3.0 in some studies

Confident. Inconsistent. None show their work. See our decisions log →