Key takeaways
- The CDC describes the 1918 pandemic as caused by an H1N1 virus with genes of avian origin, first identified in the US among military personnel in spring 1918.
- The CDC estimates about 500 million people, a third of the world's population, were infected, and at least 50 million died, about 675,000 in the United States.
- Wikipedia lists published global death estimates from about 17 million (2018) to 50 million or possibly 100 million (2005), and a 2021 estimate by John M. Barry of well above 100 million.
- The second wave, from late August 1918, was far deadlier than the first; Wikipedia says October 1918 had the highest fatality rate of the pandemic.
- Mortality was high among healthy people, including adults aged 20–40; the CDC calls this a unique feature of the pandemic.
The 1918 influenza pandemic was caused by an H1N1 virus with genes of avian origin, spread worldwide in 1918–1919, and is described by the US Centers for Disease Control and Prevention as "the most severe pandemic in recent history." The CDC estimates that about 500 million people — a third of the world's population — were infected, and that at least 50 million died, about 675,000 of them in the United States.
That "at least 50 million" is the most quoted figure, but it is one estimate among several. The useful thing to know about 1918 is how wide the honest range is, and why.
The first wave and a misleading name
Wikipedia records that the earliest probable cases were documented in March 1918 in Haskell County, Kansas, with cases in France, Germany and the United Kingdom by April. The CDC says the virus was first identified in the United States among military personnel in spring 1918, while noting there is no universal consensus on where it originated. Wikipedia adds that the limited epidemiological data make the geographic origin indeterminate, with competing hypotheses.
The name "Spanish flu" came from the news, not the disease. Wikipedia explains that wartime censors in the belligerent countries suppressed bad news to protect morale, while newspapers in neutral Spain reported the outbreak freely — so Spain looked like the epicentre. By late June 1918, The Times of London reported that "everybody thinks of it as the 'Spanish' influenza."
The first wave was relatively mild. Wikipedia gives about 75,000 flu-related deaths reported in the US in the first six months of 1918, against about 63,000 in the same period of 1915.
The deadly second wave of autumn 1918
The second wave began in the second half of August 1918 and was, Wikipedia says, much more deadly than the first; October 1918 had the highest fatality rate of the whole pandemic. In the US about 292,000 deaths were reported between September and December 1918, against about 26,000 in the same months of 1915. Troop movements at the end of the First World War helped carry it: Wikipedia describes spread from the Boston Navy Yard and Camp Devens and outward across Russia, Iran and India.
The collapse could be as fast as the rise. In Philadelphia, Wikipedia notes, 4,597 people died in the week ending 16 October, yet by 11 November influenza had almost disappeared from the city. Further waves followed in 1919 and, in some places, 1920.
Who died, and why it was unusual
The CDC lists high mortality in children under five, adults aged 20 to 40, and people 65 and older, and says the high mortality in healthy people, including those aged 20 to 40, was "a unique feature of this pandemic." Wikipedia reports that in the US in 1918–1919, 99% of pandemic influenza deaths were in people under 65 and nearly half were in adults aged 20 to 40. One explanation it gives is that older people may have had partial protection from exposure to the 1889–1890 pandemic. It also records, fairly, that the claim of unusually high young-adult mortality "has been contested."
The CDC adds that the properties that made the virus so lethal "are not well understood," even though the 1918 virus has since been reconstructed and studied. Wikipedia notes that many victims died of secondary bacterial pneumonia.
Why the death toll runs from 17 million to over 100 million
Wikipedia lists the main published global estimates:
| Year of estimate | Global deaths |
|---|---|
| 1927 | 21.6 million |
| 1991 | 25–39 million |
| 2005 | 50 million, possibly as high as 100 million |
| 2018 (American Journal of Epidemiology) | about 17 million, contested |
| 2021 (John M. Barry) | well above 100 million |
Against a world population Wikipedia gives as 1.8 to 1.9 billion, the arithmetic is straightforward. The low end, 17 million out of 1.9 billion, is about 0.9%; the high end, 100 million out of 1.8 billion, is about 5.6%. Wikipedia summarises the estimates as "between 1 and 6 percent of the population," though Barry's 2021 figure would sit above that. The CDC's 50 million out of 1.8 billion would be about 2.8%.
The range is wide because the records are uneven. India is a clear case: Wikipedia gives 12 to 17 million deaths, about 5% of the population, but also cites a study arguing that unusually high 1917 mortality and wide regional variation complicate the attribution. Russia's figure of 450,000 was called "a shot in the dark" by the epidemiologists who suggested it; another study puts it nearer 2.7 million. Even within the United States, the CDC gives about 675,000 while Wikipedia gives 500,000 to 850,000. How to read figures like these without flattening them is the theme of reading a history dataset critically, and the same problem applies to the Second World War death toll.
Some small populations suffered proportionally the most. Wikipedia records that in Western Samoa 22% of a population of 38,000 died within two months — roughly 8,360 people — and that in Tahiti 13% of the population died in one month.
What societies could and could not do
There was no influenza vaccine and there were no antibiotics for the bacterial infections that followed. The CDC says control was therefore limited to non-pharmaceutical measures — isolation, quarantine, good personal hygiene, disinfectants and limits on public gatherings — "which were applied unevenly." Wikipedia notes that differences between cities may have reflected both exposure to the milder first wave and the introduction of social distancing measures. Comparing it with an earlier catastrophe, the Black Death, shows how differently the two are documented.
This article is history, not medical guidance; for current influenza advice, consult a health authority.
World History Timeline Sim, our app, lists disease among the pressures in its Civilization Survival Mode and lets you browse major events by year. Those simulations are not history, and the app works as a companion to coursework rather than a source of figures — for numbers, go to the sources above. More history guides are in education and brain training.
Good to know
Frequently asked questions
Why is the 1918 flu called the Spanish flu if it did not start in Spain?
How many waves did the 1918 influenza pandemic have?
Who was most at risk in the 1918 pandemic?
How did countries try to control the 1918 flu?
Sources
- 1918 Pandemic (H1N1 virus) (opens in a new tab)Centers for Disease Control and Prevention (archived page) — accessed
- Spanish flu (opens in a new tab)Wikipedia — accessed
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