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1918 influenza pandemic
1918–1920· Event· Germs, drugs & genetics
Well documentedSolid records, physical evidence or scientific consensus.
An H1N1 influenza pandemic that infected about a third of the world's people and killed an estimated 17 to 50 million or more.
See it on the Technology & Medicine map →How it works
The flu spread in three main waves from spring 1918, carried by troop movements at the end of World War I. Unusually, it killed many healthy young adults, often through bacterial pneumonia that followed the virus. It was called 'Spanish' because neutral Spain's press reported it freely while warring nations censored news. Cities that closed schools, theaters and churches early, such as St. Louis, generally had fewer deaths than slower ones like Philadelphia. No flu vaccines or antibiotics existed.
Why it mattered
The deadliest pandemic of the 20th century, it cut US life expectancy by about 12 years in 1918 and still shapes how countries plan for pandemics.
How we know
Death records and newspapers from 1918–20; the virus's full genome, rebuilt by 2005 from preserved autopsy tissue and a victim buried in Alaskan permafrost. Death tolls are estimates and vary widely.
Still unknown or debated
Where it began is unknown: Kansas, France, China and Britain have all been proposed. Why it killed so many young adults is still debated.
Connections (3)
▸Sanitation and public health movement shaped the response to the 1918 influenza pandemicMostly agreed
The connection
The sanitation movement built city health departments with powers to inspect, quarantine and close places. In 1918 they used them: closing schools, theaters and churches, banning gatherings and, in some cities, ordering masks. Where these steps came early and lasted, as in St. Louis, deaths were lower than in Philadelphia, which held a huge parade first.
When and how
Cities across the US, Europe and Asia, autumn 1918; Philadelphia's Liberty Loan parade of September 28 drew about 200,000 people; St. Louis closed public places in early October.
How sure are we?
City death records, analyzed in studies such as Howard Markel and colleagues' 2007 paper on 43 US cities, link early, sustained closures to lower death rates.
Debates and open questions
How much closures and masks cut total deaths, rather than delaying them, is debated, and these lessons were argued over again during COVID-19.
▸1918 influenza pandemic was the closest precedent for the COVID-19 pandemicMostly agreed
The connection
The 1918 flu killed an estimated 17–50 million people or more; estimates vary. COVID-19 was the next airborne pandemic on a similar global scale, and officials reached for the same tools: masks, closed schools and theaters, bans on gatherings. Studies of 1918 US cities, where earlier distancing meant fewer deaths, shaped 2020 policies.
When and how
1918–20 worldwide, with famous contrasts such as Philadelphia and St. Louis; COVID-19 from Wuhan, December 2019, worldwide through 2023.
How sure are we?
2007 studies of 1918 US city records, by historian Howard Markel and others, shaped US pandemic plans that were used in 2020.
Debates and open questions
Flu pandemics in 1957 and 1968 and HIV/AIDS also killed millions, so 'closest precedent' depends on the measure; how well 1918 lessons transferred is debated.
▸Aspirin was given in possibly toxic doses during the 1918 influenza pandemicDebated
The connection
In 1918 doctors and health officials recommended aspirin for flu, sometimes 8 to 31 grams a day, far above today's limit of about 4 grams. Physician Karen Starko argued in 2009 that aspirin poisoning, which can cause fluid in the lungs, may have contributed to some deaths, especially at the October 1918 peak.
When and how
The US, Britain and elsewhere, autumn 1918; the US Surgeon General, the Navy and medical journals recommended aspirin, whose US patent had expired in 1917.
How sure are we?
Starko's 2009 paper in Clinical Infectious Diseases cites 1918 dosing advice and autopsy reports; it remains a hypothesis, not proof.
Debates and open questions
Critics note deaths also soared where aspirin was scarce, so most experts think the virus and bacterial pneumonia were the main killers.