The 1918-1920 Influenza Pandemic That Killed More People Than the First World War and Whose Geographical Origin Is Still Disputed

The 1918 influenza pandemic was the deadliest disease outbreak of the 20th century. It killed an estimated 50 million people across three waves between spring 1918 and spring 1920 — about 2.7 percent of the world’s pre-pandemic population. The death toll exceeded the combined military and civilian casualty figures of the First World War (approximately 20 million).

The “Spanish flu” name is a misnomer. Spain was neutral in the First World War and did not censor its press. Spanish newspapers reported the influenza freely from May 1918 onward; the belligerent nations (Britain, France, Germany, the United States) suppressed influenza reporting as a wartime morale measure. The international perception that the disease was “Spanish” reflected the visibility of the Spanish press coverage rather than any Spanish origin.

Where it actually started

The geographical origin of the 1918 H1N1 strain has been disputed since 1918. The three principal candidate sites are:

— Camp Funston, Kansas, United States — first documented major outbreak began 4 March 1918, transmitted with American troops to the European Western Front — Étaples military camp, France — extensive influenza-like illness from late 1916 onwards, possibly an earlier wave of the same strain — Northern China — earlier 1917 outbreaks among Chinese Labour Corps workers being shipped to support Allied logistics in Europe

The 2014 reanalysis by Mark Humphries argued for the Chinese origin; the earlier consensus had favoured Kansas. The question remains formally open.

Three waves

First wave (spring 1918): unusually contagious but with normal influenza mortality. Spread through the Western Front and the major belligerent populations across March-July 1918. Approximately 1-2 million deaths globally.

Second wave (September-December 1918): the catastrophic phase. The viral strain had mutated to a more lethal form, possibly through repeated passages through battlefield wounded who could not mount normal immune responses. The mortality pattern was W-shaped — high infant mortality, low working-age mortality in normal influenza, high elderly mortality — replaced by a W with a third peak in healthy 20-40 year olds. The cause of the young-adult mortality was cytokine storm: the immune systems of healthy adults responded too strongly to the novel virus and flooded the lung tissue with inflammatory mediators, producing acute respiratory distress syndrome. The second wave killed approximately 35-45 million globally.

Third wave (winter 1918-spring 1919): less lethal than the second but still substantial. Approximately 5-10 million deaths.

A residual fourth wave continued through spring 1920 in scattered locations.

What it did

The United States lost approximately 675,000 dead — more than its 116,000 military war dead. The 1918 American life expectancy dropped by 12 years from the pre-pandemic figure. The Indian subcontinent lost approximately 17 million dead — the single largest national casualty figure. The Western Samoan colonial population lost approximately 22 percent in two months — the highest national mortality rate documented.

The public-health response of 1918 was limited by wartime political priorities (the United States, in particular, suppressed influenza reporting in major cities to preserve war-bond sale enthusiasm) and by medical-science limitations (the influenza virus was not isolated until 1933 — 15 years after the pandemic — and the first influenza vaccine was not available until 1942). The principal effective public-health intervention was physical distancing and mask wearing; cities that implemented early closure of schools, theatres, and public gatherings had lower per-capita mortality.

2005

The viral strain that caused the 1918 pandemic was reconstructed in 2005 by the team led by the molecular pathologist Jeffery Taubenberger of the Armed Forces Institute of Pathology. The source material was preserved lung tissue from 1918 victims:

— Substantial formalin-fixed autopsy specimens from the American military’s 1918 records — Substantial frozen body tissue from a Alaskan Inuit woman named Lucy who had been buried in Brevig Mission permafrost since November 1918, where she had died with most of her village in the third wave. Her body was exhumed by Taubenberger’s collaborator Johan Hultin in 1997 — 79 years after her death — with permission from the Brevig Mission village council

The complete 1918 H1N1 genome was sequenced and published in Nature in October 2005. The reconstructed virus was tested on macaque monkeys and produced the same catastrophic respiratory disease that had killed the 1918 patients — conclusive demonstration that the 1918 virus was intrinsically more lethal than conventional influenza strains rather than only opportunistically lethal because of wartime conditions.

The reconstructed virus is held in Biosafety Level 4 containment at the US Centers for Disease Control. The subsequent research has identified the specific genomic features (the PB1-F2 protein, the NS1 protein) responsible for the cytokine-storm pathology. The 2009 H1N1 swine flu pandemic — the 21st-century descendant of the 1918 strain — was less lethal because of accumulated population immunity to the 1918 lineage.

The COVID-19 pandemic of 2020-2023 was the first comparable respiratory pandemic since 1918. It killed approximately 7 million confirmed deaths and likely more on a excess-mortality basis. The public-health response benefited from 100 years of accumulated influenza-pandemic planning, molecular virology, and vaccine technology that the 1918 response had lacked.