Spanish Flu Pandemic (1918-1920): The Deadliest Flu in History

The Spanish flu pandemic of 1918-1920 was the deadliest outbreak of influenza in recorded history. Spreading in three waves as the First World War ended, it infected an estimated 500 million people, about a third of the world’s population, and killed somewhere between 17 million and 50 million, with some estimates higher still. It struck healthy young adults with unusual ferocity and remains the benchmark against which every later pandemic is measured.

Origins: where did it begin?

Nobody knows for certain where the 1918 virus first infected humans. The first well-documented outbreak occurred at Camp Funston, a large US Army training camp at Fort Riley, Kansas. On 4 March 1918 a company cook, Albert Gitchell, reported sick with fever and aches, and within weeks more than a thousand soldiers were ill. The historian John M. Barry has argued that the virus may have come from nearby Haskell County, where a local doctor reported a severe flu outbreak earlier that year.

Other researchers point elsewhere. British army doctors described outbreaks of a severe respiratory illness at the base camp at Etaples in France in the winter of 1916-17, and some scientists have suggested that the virus travelled from northern China with labourers recruited for the Western Front. Genetic studies show that the virus was an H1N1 influenza A strain with genes of avian origin, but they have not settled where the jump to humans took place.

The name “Spanish flu” is a historical accident. Wartime censorship in Britain, France, Germany and the United States kept news of illness among troops and workers out of the papers. Spain was neutral, and its newspapers reported freely on the epidemic in May 1918, especially when King Alfonso XIII fell seriously ill.

Readers abroad concluded that Spain was the centre of the outbreak. In Spain itself the disease was often called the “French flu”, and other countries blamed their neighbours or enemies. Health organisations today avoid naming diseases after places partly because of this episode.

Three waves around the world

The first wave, in spring and early summer 1918, was relatively mild. It spread through army camps in the United States, crossed the Atlantic with troop ships and swept through the armies on the Western Front, where it was sometimes called “three-day fever”. Death rates were not much higher than in a normal flu season.

The second wave, from roughly September to November 1918, was catastrophic. A more lethal form of the virus appeared almost simultaneously in late August in Freetown in Sierra Leone, Brest in France and Boston in the United States. In October 1918 alone, the United States recorded close to 200,000 deaths. Victims could turn blue from lack of oxygen, a sign called heliotrope cyanosis, and some died within a day or two of falling ill.

A third wave followed in the winter and spring of 1919, still deadly but less so than the autumn. Further local outbreaks occurred in 1920 in places such as Peru, Japan and parts of Scandinavia, after which the pandemic faded as immunity spread through the population.

Who died, and why

Ordinary flu kills mainly infants and the elderly, producing a U-shaped curve of deaths by age. In 1918 the curve was W-shaped: deaths were also very high among adults aged about 20 to 40. Pregnant women were especially at risk. Why healthy young people died so often is still debated. One theory is that their strong immune systems overreacted, flooding the lungs with fluid; another is that older people had partial protection from an earlier, related flu strain.

Studies of preserved lung tissue show that most victims did not die from the virus alone but from bacterial pneumonia that followed it. In the age before antibiotics, there was no effective treatment. Doctors did not even know that a virus was the cause: many believed the culprit was a bacterium, and the human influenza virus was not isolated until 1933.

The burden fell unevenly. India suffered the greatest loss of life, with estimates commonly in the range of 12 to 20 million deaths. Some isolated communities were devastated: in Western Samoa, where the disease arrived by ship in November 1918, around a fifth of the population died, while neighbouring American Samoa avoided deaths by imposing a strict quarantine.

By the numbers

All figures are estimates; records were incomplete in many countries, especially in Africa and Asia.

How societies responded

Public health measures varied widely. Many cities closed schools, theatres, churches and saloons, banned public gatherings, and required or encouraged gauze masks. In the United States, the Surgeon General Rupert Blue urged local authorities to act, but decisions were made city by city.

The contrast between Philadelphia and St Louis became a famous case study. Philadelphia held a large Liberty Loan parade on 28 September 1918 and suffered a sharp spike in deaths soon afterwards; St Louis closed public places early and had a much lower peak. Later research suggested that cities that introduced several measures early, and kept them in place longer, tended to have lower death rates, although historians caution that many other factors were involved.

The war shaped the pandemic at every stage. Crowded camps, trenches and troop ships spread the virus, while censorship delayed warnings. Thousands of soldiers died of influenza in the final weeks of the war, and public celebrations of the Armistice of 11 November 1918 brought crowds together at the height of the second wave.

Famous victims and survivors

The pandemic killed people from every walk of life. Among the well-known victims were the Austrian painter Egon Schiele, who died on 31 October 1918, three days after his pregnant wife; the French poet Guillaume Apollinaire, who died on 9 November 1918; and the German sociologist Max Weber, who died of pneumonia in 1920.

Many prominent people fell ill and recovered, including King Alfonso XIII of Spain, the Norwegian painter Edvard Munch, who painted a self-portrait during his illness, and the young Walt Disney. The US president Woodrow Wilson was severely ill during the Paris Peace Conference in April 1919, and many historians believe he had influenza.

What science learned

For decades the 1918 virus was a mystery. In 1951 the scientist Johan Hultin travelled to Brevig Mission in Alaska, where most of the adult population had died in November 1918 and been buried in the permafrost, but he could not recover live virus. In the 1990s a team led by Jeffery Taubenberger at the US Armed Forces Institute of Pathology began extracting fragments of viral genetic material from preserved autopsy samples.

In 1997 Hultin, then in his seventies, returned to Brevig Mission and recovered lung tissue from a victim frozen in the ground. Using these samples, researchers completed the sequence of the virus’s eight gene segments and published it in 2005. The same year, scientists at the US Centers for Disease Control and Prevention reconstructed the virus under high-security conditions and confirmed that it was exceptionally lethal in animal tests.

This work showed that the 1918 strain was the ancestor of later H1N1 and other flu viruses, including the strains behind the 1957 and 1968 pandemics and, in part, the 2009 swine flu pandemic. It also shaped modern pandemic planning, from vaccine stockpiles to the “flatten the curve” strategies used during the COVID-19 pandemic.

Myths and facts

• Myth: The flu started in Spain. Fact: Spain was simply where it was reported openly; the origin remains unknown, but Spain is not considered a likely candidate.
• Myth: The First World War was far deadlier than the flu. Fact: On most estimates the pandemic killed more people, since the war’s military and civilian deaths are usually put at around 15 to 22 million, but both figures are uncertain.
• Myth: It was only a problem in Europe and North America. Fact: The heaviest losses were in Asia, Africa and the Pacific, with India alone accounting for a large share of all deaths.

Timeline

• 1918, 4 March: A cook at Camp Funston, Kansas, reports sick in one of the first documented outbreaks.
• 1918, May: Spanish newspapers report widely on the epidemic; King Alfonso XIII falls ill.
• 1918, late August: The deadlier second wave appears in Freetown, Brest and Boston.
• 1918, 28 September: A Liberty Loan parade in Philadelphia is followed by a surge in deaths.
• 1918, October: The deadliest month of the pandemic in the United States and many other countries.
• 1918, November: Influenza reaches Western Samoa and Brevig Mission, Alaska, with devastating results.
• 1919, January-April: A third wave strikes many countries.
• 1920: Late local outbreaks; the pandemic fades.
• 2005: Scientists publish the full genome of the 1918 virus and reconstruct it in a laboratory.

Why it matters

The 1918 pandemic killed more people in about two years than any other single outbreak of the twentieth century and reshaped families and communities around the world. Along with earlier pandemics such as the Russian flu of 1889, it taught lasting lessons about how quickly a new virus can travel, why early public health measures matter, and how censorship and complacency can cost lives.