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Spanish flu: The deadliest pandemic in history

Beds with patients in an emergency hospital in Camp Funston, Kansas, in the midst of the Spanish flu pandemic.
An emergency hospital during Spanish flu influenza pandemic, Camp Funston, Kansas, c. 1918
(Image: © Otis Historical Archives, National Museum of Health and Medicine)

In 1918, a strain of influenza known as Spanish flu caused a global pandemic, spreading rapidly and killing indiscriminately. Young, old, sick and otherwise-healthy people all became infected, and at least 10% of patients died. 

Estimates vary on the exact number of deaths caused by the disease, but it is thought to have infected a third of the world's population and killed at least 50 million people, making it the deadliest pandemic in modern history. Although at the time it gained the nickname "Spanish flu," it's unlikely that the virus originated in Spain.

What caused the Spanish flu? 

The outbreak began in 1918, during the final months of World War I, and historians now believe that the conflict may have been partly responsible for spreading the virus. On the Western Front, soldiers living in cramped, dirty and damp conditions became ill. This was a direct result of weakened immune systems from malnourishment. Their illnesses, which were known as "la grippe," were infectious, and spread among the ranks. Within around three days of becoming ill, many soldiers would start to feel better, but not all would make it. 

During the summer of 1918, as troops began to return home on leave, they brought with them the undetected virus that had made them ill. The virus spread across cities, towns and villages in the soldiers' home countries. Many of those infected, both soldiers and civilians, did not recover rapidly. The virus was hardest on young adults between the ages of 20 and 30 who had previously been healthy. 

In 2014, a new theory about the origins of the virus suggested that it first emerged in China, National Geographic reported. Previously undiscovered records linked the flu to the transportation of Chinese laborers, the Chinese Labour Corps, across Canada in 1917 and 1918. The laborers were mostly farm workers from remote parts of rural China, according to Mark Humphries' book "The Last Plague" (University of Toronto Press, 2013). They spent six days in sealed train containers as they were transported across the country before continuing to France. There, they were required to dig trenches, unload trains, lay tracks, build roads and repair damaged tanks. In all, over 90,000 workers were mobilized to the Western Front. 

Humphries explains that in one count of 25,000 Chinese laborers in 1918, some 3,000 ended their Canadian journey in medical quarantine. At the time, because of racial stereotypes, their illness was blamed on "Chinese laziness" and Canadian doctors did not take the workers' symptoms seriously. By the time the laborers arrived in northern France in early 1918, many were sick, and hundreds were soon dying.

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typist wearing a mask to prevent influenza during the Spanish flu pandemic, 1918

Typist wearing a mask to prevent influenza, New York, 1918. (Image credit: National Archives )
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A nurse collects water wearing a mask as a protection against influenza

A nurse collects water at a special camp to treat infected servicemen, Brookline, Massachusetts. (Image credit: National Archives)
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Men gargle with salt water as a preventative measure against influenza, Fort Dix, New Jersey

Men gargle with salt water as a preventative measure against influenza, Fort Dix, New Jersey. (Image credit: National Archives)
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Female conductors wearing influenza masks, New York, 1918

Conductors wearing influenza masks, New York, 1918. (Image credit: National Archives)
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Clerks at work with influenza masks, New York, Oct. 1918

Clerks at work with influenza masks, New York, Oct. 1918. (Image credit: National Archives)
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A street sweeper in New York wearing a protective mask

A street sweeper in New York wearing a protective mask. (Image credit: National Archives)
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A U.S. soldier receives preventative treatment for the flu

A U.S. soldier receives preventative treatment for the flu. (Image credit: National Archives)
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A police officer conducts traffic in New York during the Spanish flu pandemic, 1918

A police officer conducts traffic in New York during the Spanish flu pandemic, 1918. (Image credit: National Archives)
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A postal worker wearing a gauze mask, New York, 1918

A postal worker wearing a gauze mask, New York, 1918. (Image credit: National Archives)

Why was it called the Spanish flu?

Spain was one of the earliest countries where the epidemic was identified, but historians believe this was likely a result of wartime censorship. Spain was a neutral nation during the war and did not enforce strict censorship of its press, which could therefore freely publish early accounts of the illness. As a result, people falsely believed the illness was specific to Spain, and the name "Spanish flu" stuck.

Even in late Spring 1918, a Spanish news service sent word to Reuters' London office informing the news agency that "a strange form of disease of epidemic character has appeared in Madrid. The epidemic is of a mild nature, no deaths having been reported," according to Henry Davies' book "The Spanish Flu," (Henry Holt & Co., 2000). Within two weeks of the report, more than 100,000 people had become infected with the flu.

Related: World War I: The science of communications

The illness struck the king of Spain, Alfonso XIII, along with leading politicians. Between 30% and 40% of people who worked or lived in confined areas, such as schools, barracks and government buildings, became infected. Service on the Madrid tram system had to be reduced, and the telegraph service was disturbed, in both cases because there were not enough healthy employees available to work. Medical supplies and services couldn't keep up with demand. 

The term "Spanish influenza" rapidly took hold in Britain. According to Niall Johnson's book "Britain and the 1918-19 Influenza Pandemic" (Routledge, 2006), the British press blamed the flu epidemic in Spain on the Spanish weather: "… the dry, windy Spanish spring is an unpleasant and unhealthy season," read one article in The Times. It was suggested that microbe-laden dust was being spread by the high winds in Spain, meaning that Britain's wet climate might stop the flu from spreading there.

Members of the Red Cross give a demonstration at an Emergency Ambulance Station in Washington, D.C., during the influenza pandemic of 1918 (Image credit: Library of Congress)

What were the symptoms of the flu?

Initial symptoms of the illness included a sore head and tiredness, followed by a dry, hacking cough; a loss of appetite; stomach problems; and then, on the second day, excessive sweating. Next, the illness could affect the respiratory organs, and pneumonia could develop. Humphries explains that pneumonia, or other respiratory complications brought about by the flu, were often the main causes of death. This explains why it is difficult to determine exact numbers killed by the flu, as the listed cause of death was often something other than the flu. 

By the summer of 1918, the virus was quickly spreading to other countries in mainland Europe. Vienna and Budapest, Hungary, were suffering, and parts of Germany and France were similarly affected. Many children in Berlin schools were reported ill and absent from school, and absences in armament factories reduced production. 

By June 25, 1918, the flu epidemic in Spain had reached Britain. In July, the epidemic was hitting the London textile trade hard, with one factory having 80 out of 400 workers go home sick in one evening alone, according to "The Spanish Influenza Pandemic of 1918-1919: New Perspectives" (Routledge, 2003). In London, reports on government workers absent due to the flu range from 25% to 50% of the workforce. 

The epidemic had rapidly become a pandemic, making its way around the world. In August 1918, six Canadian sailors died on the St. Lawrence River. In the same month, cases were reported among the Swedish army, then in the country's civilian population and also among South Africa's laboring population. By September, the flu had reached the U.S. through Boston harbor.

Officials feared mass hysteria in major cities. Citizens were urged to stay indoors and avoid congested areas. Here, policemen patrol the streets to ensure public safety (Image credit: The National Archives)

What advice were people given? 

Doctors were at a loss as to what to recommend to their patients; many physicians urged people to avoid crowded places or simply other people. Others suggested remedies included eating cinnamon, drinking wine or even drinking Oxo's meat drink (beef broth). Doctors also told people to keep their mouths and noses covered in public. At one point, the use of aspirin was blamed for causing the pandemic, when it might actually have helped those infected. 

On June 28, 1918, a public notice appeared in the British papers advising people of the symptoms of the flu; however, it turned out this was actually an advertisement for Formamints, a tablet made and sold by a vitamin company. Even as people were dying, there was money to be made by advertising fake "cures." The advert stated that the mints were the "best means of preventing the infective processes" and that everyone, including children, should suck four or five of these tablets a day until they felt better. 

Americans were offered similar advice about how to avoid getting infected. They were advised not to shake hands with others, to stay indoors, to avoid touching library books and to wear masks. Schools and theaters closed, and the New York City Department of Health strictly enforced a Sanitary Code amendment that made spitting in the streets illegal, according to a review published in the journal Public Health Reports

World War I resulted in a shortage of doctors in some areas, and many of the physicians who were left became ill themselves. Schools and other buildings became makeshift hospitals, and medical students had to take the place of doctors in some instances.

Nurses preparing masks to prevent the spread of influenza in 1918. (Image credit: National Archives )

How many people died? 

By the spring of 1919, the numbers of deaths from the Spanish flu were decreasing. Countries were left devastated in the wake of the outbreak, as medical professionals had been unable to halt the spread of the disease. The pandemic echoed what had happened 500 years earlier, when the Black Death wreaked chaos around the world. 

Nancy Bristow's book "American Pandemic: The Lost Worlds of the 1918 Influenza Epidemic" (Oxford University Press, 2016) explains that the virus affected as many as 500 million people around the world. At the time, this represented a third of the global population. As many as 50 million people died from the virus, though the true figure is thought to be even higher. 

Bristow estimates that the virus infected as much as 25% of the U.S. population, and among members of the U.S. Navy, this number reached up to 40%, possibly due to the conditions of serving at sea. The flu had killed 200,000 Americans by the end of October 1918, and Bristow claims that the pandemic killed over 675,000 Americans in total. The impact on the population was so severe that in 1918, American life expectancy was reduced by 12 years. 

Bodies piled up to such an extent that cemeteries were overwhelmed and families had to dig graves for their relatives. The deaths created a shortage of farmworkers, which affected the late summer harvest. As in Britain, a lack of staff and resources put other services, such as waste collection, under pressure.

The pandemic spread to Asia, Africa, South America and the South Pacific. In India, the mortality rate reached 50 deaths per 1,000 people — a shocking figure. 

How does this compare to seasonal flu?

The Spanish flu remains the most deadly flu pandemic to date by a long shot, having killed an estimated 1% to 3% of the world's population. 

The most recent comparable flu pandemic occurred in 2009 to 2010, after a new form of the H1N1 influenza strain appeared. The disease was named the "swine flu" because the virus that causes it is similar to one found in pigs (not because the virus came from pigs). 

The swine flu caused respiratory illnesses that killed an estimated 151,700-575,400 people worldwide in the first year, according to the Centers for Disease Prevention and Control. That was about 0.001% to 0.007% of the world's population, so this pandemic was much less impactful than the 1918 Spanish flu pandemic. About 80% of the deaths caused by swine flu occurred in people younger than 65, which was unusual. Typically, 70% to 90% of deaths caused by seasonal influenza are in people older than 65. 

A vaccine for the influenza strain that causes swine flu is now included in annual flu vaccines. People still die from the flu every year, but the numbers are far lower, on average, compared to those for the swine flu or Spanish flu pandemics. Annual epidemics of seasonal flu result in about 3 million to 5 million cases of severe illness and about 290,000 to 650,000 deaths, according to the World Health Organization

Additional resources: 

  • Find more information on how the World Health Organization manages epidemics and pandemics. 
  • Learn what the top 10 causes of death are, from the World Health Organization.
  • Read more about influenza pandemics and their effects on the U.S. population, from the CDC.  

This article was adapted from a previous version published in All About History magazine, a Future Ltd. publication. To learn more about some of history's most incredible stories, subscribe to All About History magazine.

  • gorgeswalker
    One of the saddest realities of the 1918-1919 Flu Pandemic was that young people with healthy immune systems were most affect. Their immune response generated a cascade of cytokine storm and that inflammation, in addition to any underlying lack of healthy food, nutrients, sunshine, is what killed them. If they had been megadosed with C and given D many would have survived. May their souls rest in peace.
    Reply
  • Agamoto
    Except that’s not what killed them at all. What killed them were The bacterial infections that took over where the virus left off. A one two knockout punch.
    Reply
  • gorgeswalker
    Agamoto said:
    Except that’s not what killed them at all. What killed them were The bacterial infections that took over where the virus left off. A one two knockout punch.
    It was a cytokine storm, the cascade of inflammation, as documented and researched here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4711683/See conclusions.
    Reply
  • Agamoto
    gorgeswalker said:
    It was a cytokine storm, the cascade of inflammation, as documented and researched here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4711683/See conclusions.

    From my understanding, the effect of the cytokine storm was the massive effusion of fluid into alveoli, the consequence of which was secondary bacterial pneumonia progressing to organ failure.

    https://www.ncbi.nlm.nih.gov/pubmed/18710327
    Familiar name there in the author list, Good ol' Tony Fauci himself.
    Reply
  • Omar1
    admin said:
    Over 100 years ago, a killer strain of the influenza virus infected over a third of the world's population.

    Spanish flu: The deadliest pandemic in history : Read more
    My strongest hope is for concerned people here on this forum to read the article and then spread the word of the results and duration of this last pandemic through social media such as Facebook and Twitter. Like myself, I am quite sure there are so many out there who have little or no knowledge of the "Spanish Flu" pandemic of 1918-1919! The number of deaths and the duration of that pandemic was far greater than anyone expected and there had to be reasons for that duration.

    The one fear that I have, as a 77 year old senior, is that people will get the idea that this will be "all over" within the next few weeks or months, and that may not be the case at all. If we open up the work places, restaurants, and most of the other closed environment areas of human congregation too early, this pandemic could re-establish itself again and then it's simply more of the same as we have endured for the past few months.

    We probably have the technology and the advances to find a solution to this problem but it will take time, with the governmental and private enterprise "restraints" we have in place today, But we need to also make sure that the ENTIRE public, young and old, is advised and also convinced that the very BEST avenue to pursue is to allow enough time for technology to "work" before returning to "normal" again. Otherwise, we may face a second "flare-up" of this pandemic as people try to pick up their lives and start working again.

    How many people do you come in contact with, on a daily basis, are "carriers" of Covid-19 and do NOT even realize that they are unknowingly infected and passing it along to those close to them? I have worn a mask since I was initially forced to go to places in which I had no control of other's medical situation. It wasn't because I was buying into any prestated pandemic control methods but it was simply common sense in my mind that I would protect myself from any unknown carriers of the Covid virus. In a perfect world, if we all decided to wear masks in public, we would be protecting ourselves against anyone else at all times AND protecting anyone who forgot their mask or otherwise didn't choose to wear one from accidently coming into contact with anyone else who didn't know that THEY were carrying the virus.

    I will continue to follow my instincts until and unless I am convinced that all is safe and over with at least in my immediate area. That will be determined as time dictates and the frequency of occurrence diminishes to a tolerable level or is eradicated altogether.
    Reply
  • tedward outward
    Not sure of the accuracy of the premise. The first plague that hit the world in the 1300s killed between 100-300M people, over 4 years. 45–50% of the European population died of the plague. Spanish Flu not even close to these numbers, let alone % of world population mortality. Authors need to update or revise.
    Reply
  • Lethe
    Hmmm. I've been poking around a bit looking for the answer to the obvious question (at least to me): What ENDED the Great Spanish Influenza Pandemic? Not a single article I've managed to locate and skim has answered that question definitively, in fact it isn't really brought up at all other than to note that it ended in or around a particular month/year.

    It seems to have simply petered out over the course of 2-3 years and a number of 'waves.' Herd immunity? A combination of herd immunity and containment efforts (masking, antiseptic measures, social distancing)?

    Given the breadth and severity of its spread, it seems unlikely that it would simply, in the unfortunate words of my president, "just disappear."
    Reply
  • DLKirk
    Read your comments with interest. When you read studies, read each and every word before you.

    Notice words such as: suggests, many, sometimes, and so forth.
    The conclusion states,"... died from overwhelming viral pneumonia and serious complications caused by cytokine storm."

    Suggests, "death from the complications that arose due to cytokine storms, in man" . . . . "how an enhanced broad immune response can sometimes worsen the outcome" of disease

    The Spanish flu was brought to the USA from Soldiers returning home. I doubt the lack of Vitamin D, in that epidemic, because most folks with a little land back then needed to plant some edibles, and those on farms of even small sizes general had milk cows at least so they had milk and butter for their table, not to mention the sunshine when working outdoors for their garden, to wash clothes and hang them to dry, etc.

    Vit. C may have been a little scarce in some areas, but not in many others. Let's not forget that Vit. C is found in foods other than Citrus fruits.

    The Spanish flu epidemic lasted approx. 2-years before it ended, killing (if I recall) close to 500 million people worldwide. My uncle was one of them, the middle son between my Uncle other uncle and my own father.

    And mustn't forget genetics has a lot to say about who gets infected, what it infects, and how bad it may be. We've this with COVID-19, but don't think a mild
    case means the person is will do this well with another flu. Covid is the Novelest of the Novel viruses in the rapid manner it mutated and the way symptoms changed.
    Was this the original Covid, or was it one of the hybrids with SARS, and what sort of combinations were created from this? This particular epidemic was difficult to keep up with, even for a retired Health Professional "hunkering down" and on the computer for a long shift posting pertinent finds online, or providing current information to Twitter, or Facebook; the only social media I could easily post to.

    One thing to remember about Health studies. . . .the finding are all too often reversed in a few years. Consider them, look for the words that mean "maybe" and collect more data as you move on.
    Reply
  • Mitch
    Good article, thoroughly enjoyed reading through it. Some numbers and some information are missing or dumbed down a bit but I really liked it. Good sources and well organized 👍 Sidenote: Would highly recommend what's been my favourite book for over a year now. John M. Barry's 'The Great Influenza' is probably the best book I've ever read, and I'd highly recommend it :)
    Reply