The Spanish flu (1918-20): The global impact of the largest influenza pandemic in history (2023)

by Max Roser

In the last 150 years the world has seen an unprecedented improvement in health. The visualization shows that in many countries life expectancy,which measures the average age of death, doubled from around 40 years or less to more than 80 years. This was not just an achievement across these countries; life expectancy has doubled in all regions of the world.

What also stands out is how abrupt and damning negative health events can be. Most striking is the large, sudden decline of life expectancy in 1918, caused by an unusually deadly influenza pandemic that became known as the ‘Spanish flu’.

To make sense of the fact life expectancy declined so abruptly, one has to understand what it measures. Period life expectancy, which is the precise name for this measure, only looks at the mortality pattern in one particular year and then captures this snapshot of population health as the average age of death of a hypothetical cohort of people for which that year’s mortality pattern would remain constant throughout their entire lifetimes. Period life expectancy is a measure of the population’s health in one year. [If you want to understand this in more detail you find our discussion of it here.]

This influenza outbreak wasn’t restricted to Spain and it didn’t even originate there (recent research by Olson et al. (2005) suggests that the epidemic originated in New York due to evidence of a pre-pandemic wave of the virus in that city).1

But it was named as such because Spain was neutral in the First World War (1914-18), which meant it was free to report on the severity of the pandemic, while countries that were fighting tried to suppress reports on how the influenza impacted their population to maintain morale and not appear weakened in the eyes of the enemies.

The influenza outbreak started in the Northern Hemisphere in the spring of 1918. The virus spread rapidly and eventually reached all parts of the world: the epidemic became a pandemic.2

(Video) Deadliest Plague of the 20th Century: Flu of 1918

Even in a much less-connected world the virus eventually reached extremely remote places such as the Alaskan wilderness and Samoa in the middle of the Pacific islands.3

While peak mortality was reached in 1918 the pandemic did not end until two years later in late 1920.

The global death count of the flu today

To have a context for the severity of influenza pandemics it might be helpful to know the death count of a typical flu season. Current estimates for the annual number of deaths from influenza are around 400,000 deaths per year. Paget et al (2019) suggest an average of 389,000 with an uncertainty range 294,000 from 518,000.4

This means that in recent years the flu was responsible for the death of 0.0052% of the world population – one person out of 18,750.5 Even in comparison to the low estimate for the death count of the Spanish flu (17.4 million) this pandemic, more than a century ago, caused a death rate that was 182 -times higher than today’s baseline. Further below I will briefly discuss similarities and differences with the Coronavirus (COVID-19) in 2019/20.

Click to open interactive version

How many people died in the Spanish flu and other influenza pandemics?

Global deaths of the Spanish flu

Several research teams have worked on the difficult problem of reconstructing the global health impact of the pandemic. There is now a lot of variability in these estimates and while the academic discussions continue the range of estimates gives us an understanding of the severity of the event.

The visualization here shows the available estimates from the different research publication discussed in the following.

Patterson and Pyle (1991) estimated that between 24.7 and 39.3 million died from the pandemic.6

(Video) The Spanish flu: the biggest pandemic in modern history

The widely cited study by Johnson and Mueller (2002) arrives at a much higher estimate of 50 million global deaths. But the authors suggest that this could be an underestimation and that the true death toll was as high as 100 million.7

The more recent study by Spreeuwenberg et al. (2018) concluded that earlier estimates have been too high. Their own estimate is 17.4 million deaths.8

Global death rate

How do these estimates compare with the size of the world population at the time? How large was the share who died in the pandemic?

Estimates suggest that the world population in 1918 was 1.8 billion.

Based on this, the low estimate of 17.4 million deaths by Spreeuwenberg et al. (2018) implies that the Spanish flu killed almost 1% (0.95%) of the world population.9

If we rely on the estimate of 50 million deaths published by Johnson and Mueller, it implies that the Spanish flu killed 2.7% of the world population. And if it was in fact higher– 100 million as these authors suggest – then the global death rate would have been 5.4%.10

The world population was growing by around 13 million every year in this period which suggests that the period of the Spanish flu was likely the last time in history when the world population was declining.11

Other large influenza pandemics

The Spanish flu pandemic was the largest, but not the only large recent influenza pandemic. Two decades before the Spanish flu the Russian flu pandemic (1889-1894) is believed to have killed 1 million people.12

Estimates for the death toll of the “Asian Flu” (1957-1958) vary between 1.5 and 4 million. Gatherer (2009)13 published the estimate of 1.5 million, while Michaelis et al. (2009) published an estimate of 2–4 million.14

According to a WHO publication the “Hong Kong Flu” (1968-1969) killed between 1 and 4 million people.15

Michaelis et al. (2009) published a lower estimate of 1–2 million.16

The Russian Flu pandemic of 1977-78 was caused by the same H1N1 virus that caused the Spanish flu. According to Michaelis et al. (2009) around 700,000 died worldwide.17

What becomes clear from this overview are two things: influenza pandemics are not rare, but the Spanish flu of 1918 was by far the most devastating influenza pandemic in recorded history.

(Video) The Spanish Flu of 1918: the history of a deadly pandemic and lessons for coronavirus

The Spanish flu (1918-20): The global impact of the largest influenza pandemic in history (2)

The impact of the Spanish flu pandemic on different age groups

This last visualization here shows the life expectancy in England and Wales by age. The red line shows the life expectancy for a newborn, with the rainbow-colored lines above showing how long a person could expect to live once they had reached that given, older, age. The light green line, for example, represents the life expectancy for children who had reached age 10.

It shows that life expectancy increased at all ages, which means that the often-heard assertion that life expectancy ‘only’ increased because child mortality declined is not true. This long-term rise of life expectancy at all ages is the focus of this accompanying text here.

With respect to the impact of the Spanish flu it is striking that the visualization shows that the pandemic had very little impact on older people. While the life expectancy at birth and at young ages declined by more than ten years, the life expectancy of 60- and 70-year olds saw no change. This is at odds with what we would expect: older populations tend to be most vulnerable to influenza outbreaks and respiratory infections. If we look at mortality for both lower respiratory infections (pneumonia) and upper respiratory infections today, death rates are highest for those who are 70 years and older.

One reason why this pandemic was so devastating was that young people accounted for a large share of the population.

Why were older people so resilient to the 1918 pandemic? The research literature suggests that this was the case because older people had lived through an earlier flu outbreak – the already discussed ‘Russian flu pandemic’ of 1889–90 – which gave those who lived through it some immunity for the later outbreak of the Spanish flu.18

The earlier 1889-90 pandemic might have given the older population some immunity, but was a destructive event in itself. According to Smith 132,000 people died in England, Wales, and Ireland alone.19

The Spanish flu (1918-20): The global impact of the largest influenza pandemic in history (3)

How the Spanish flu differs from the Coronavirus outbreak in 2020

(Video) The Spanish Flu & How The World Recovered (1918-1929) History Documentary

Writing in early March 2020 it is an obvious question to ask how the ongoing outbreak of COVID-19 compares. We have a page dedicated to the research and data on the Coronavirus outbreak.

When comparing COVID-19 with the Spanish flu, there are a number of important differences that should be considered:

They are not the same disease and the virus causing these diseases are very different. The virus that causes COVID-19 is a coronavirus, not an influenza virus that caused the Spanish flu and the other influenza pandemics listed above.

The age-specific mortality seems to be very different. As we’ve seen above, the Spanish flu in 1918 was especially dangerous to infants and younger people. The new coronavirus that causes COVID-19 appears to be most lethal to the elderly, based on early evidence in China.20

We’ve also seen above that during the Spanish flu many countries tried to suppress any information about the influenza outbreak. Today the sharing of data, research, and news is certainly not perfect, but very different and much more open than in the past.

But it is true that the world today is much better connected. In 1918 it was railroads and steamships that connected the world. Today planes can carry people and viruses to many corners of the world in a very short time.

Differences in health systems and infrastructure also matter. The Spanish flu hit the world in the days before antibiotics were invented; and many deaths, perhaps most, were not caused by the influenza virus itself, but by secondary bacterial infections. Morens et al (2008) found that during the Spanish flu “the majority of deaths … likely resulted directly from secondary bacterial pneumonia caused by common upper respiratory–tract bacteria.”21

And not just health systems were different, but also the health and living conditions of the global population. The 1918 hit a world population of which a very large share was extremely poor – large shares of the population were undernourished, in most parts of the world the populations lived in very poor health, and overcrowding, poor sanitation and low hygiene standards were common. Additionally the populations in many parts of the world were weakened by a global war. Public resources were small and many countries had just spent large shares of their resources on the war.

While most of the world is much richer and healthier now, the concern today too is that it is the poorest people that are going to be hit hardest by the COVID-19 outbreak.22

These differences suggest that one should be cautious in drawing lessons from the outbreak a century ago.

But the Spanish flu reminds us just how large the impact of an pandemic can be, even in countries that had already been successful in improving population health. A new pathogen can cause terrible devastation and lead to the death of millions. For this reason the Spanish flu has been cited as a warning and as a motivation to prepare well for large pandemic outbreaks, which have been considered likely by many researchers.23


What was the Spanish flu and how did it affect the world? ›

The Spanish flu was a pandemic — a new influenza A virus that spread easily and infected people throughout the world. Because the virus was new, very few people, if any, had some immunity to the disease. From 1918 to 1919, the Spanish flu infected an estimated 500 million people globally.

What impact did the Spanish flu have in 1918-1919? ›

It is estimated that about 500 million people or one-third of the world's population became infected with this virus. The number of deaths was estimated to be at least 50 million worldwide with about 675,000 occurring in the United States.

What caused the 1918 influenza pandemic? ›

The 1918 influenza pandemic was the most severe pandemic in recent history. It was caused by an H1N1 virus with genes of avian origin. Although there is not universal consensus regarding where the virus originated, it spread worldwide during 1918-1919.

How did the 1918 flu spread? ›

Outbreaks of the influenza pandemic of 1918-1919 occurred in nearly every inhabited part of the world. Although it remains uncertain where the virus first emerged, it quickly spread through western Europe and around the world—first in ports, then from city to city along main transportation routes.

What was a major effect of the 1918 influenza pandemic? ›

The flu afflicted over 25 percent of the U.S. population. In one year, the average life expectancy in the United States dropped by 12 years. It is an oddity of history that the influenza epidemic of 1918 has been overlooked in the teaching of American history.

How did influenza affect the world? ›

The influenza pandemic of 1918-1919 killed more people than the Great War, known today as World War I (WWI), at somewhere between 20 and 40 million people. It has been cited as the most devastating epidemic in recorded world history.

How did the 1918 flu crisis affect the US? ›

In the United States, the flu's toll was much lower: a 1.5 percent decline in GDP and a 2.1 percent drop in consumption. The decline in economic activity combined with elevated inflation resulted in large declines in the real returns on stocks and short-term government bonds.

How did Spanish flu impact public health? ›

Influenza pandemics have occurred periodically in human populations, with three pandemics in the 20th century. The 1918 influenza pandemic resulted in unprecedented mortality, with an estimated 500,000–675,000 deaths in the U.S. and 50–100 million deaths worldwide (1–3).

How the Spanish flu affected the economy? ›

During both the pandemics, the economies registered a fall in the per capita GDP. Maddison Project Database (2020), as depicted in Figure 3, suggests that during the influenza pandemic, per capita GDP fell from US$1111 in 1917 to US$968 in 1918. However, in the later years, the per capita GDP began to rise.

How did they try to stop the spread of the flu? ›

Get the flu vaccine. Wash your hands often, especially before eating and after coughing, sneezing, or blowing your nose. Keep your sneezes and coughs to yourself (use a tissue or your elbow instead of your hand). Keep your hands out of your eyes, mouth, and nose.

How did they treat Spanish flu? ›

The treatment was largely symptomatic, aiming to reduce fever or pain. Aspirin, or acetylsalicylic acid was a common remedy. For secondary pneumonia doses of epinephrin were given. To combat the cyanosis physicians gave oxygen by mask or some injected it under the skin (JAMA, 10/3/1918).

What problems does influenza cause? ›

Other possible serious complications triggered by flu can include inflammation of the heart (myocarditis), brain (encephalitis) or muscle tissues (myositis, rhabdomyolysis), and multi-organ failure (for example, respiratory and kidney failure).

What are the causes and effects of influenza? ›

The flu is caused by an influenza virus. Most people get the flu when they breathe in tiny airborne droplets from the coughs or sneezes of someone who has the flu. You can also catch the flu if you touch something with the virus on it, and then touch your mouth, nose, or eyes. People often confuse colds and flu.

How does influenza cause damage? ›

Influenza can primarily cause severe pneumonia, but it can also present in conjunction with or be followed by a secondary bacterial infection, most commonly by S. aureus and S. pneumoniae. Influenza is associated with a higher predisposition to bacterial sepsis and ARDS.

How did America respond to the Spanish flu? ›

When influenza appeared in the United States in 1918, Americans responded to the incursion of disease with measures used since Antiquity, such as quarantines and social distancing. During the pandemic's zenith, many cities shut down essential services.

How did the Spanish flu affect modern medicine? ›

A major new development since the pandemic is of course, the flu vaccination, among other vaccines. Created in 1938 with fertilized chicken eggs, several options are now available to fight against influenza, including high-dose vaccines for seniors and egg-free varieties.

Why was the Spanish flu difficult to treat? ›

Without previous exposure to the virus, the body's immune system would not have been able to produce an efficient response. Just as importantly, however, the virus itself had not yet fully adapted to life in a human body. Contrary to expectations, it is not normally within a flu virus's interests to kill the host.

How did the Spanish flu improve medicine? ›

The search for the virus, and a vaccine to prevent the influenza, led to a number of other discoveries. It created tools for the development of other vaccines. Today we still use fertile eggs to grow viruses. It also led to our understanding of the nature of genes and the chemicals that encode them.

What organs does the flu affect? ›

Overview. Flu (influenza) is an infection of the nose, throat and lungs, which are part of the respiratory system. Influenza is commonly called the flu, but it's not the same as stomach "flu" viruses that cause diarrhea and vomiting.

What is good for flu? ›

Rest and fluids can help with your fever symptoms, but you can also take a fever reducer like acetaminophen to temporarily relieve your fever symptoms. Acetaminophen also helps to reduce pain, which will come in helpful since headache and muscle aches also often accompany fevers from the flu.

Why did the Spanish flu spread so quickly? ›

Lack of Quarantines Allowed Flu to Spread and Grow

Harris believes that the rapid spread of Spanish flu in the fall of 1918 was at least partially to blame on public health officials unwilling to impose quarantines during wartime.

Is there a cure for the Spanish flu today? ›

Are current antivirals and vaccines effective against the 1918 H1N1 virus? Yes. Oseltamivir (Tamiflu® or generic), has been shown to be effective against similar influenza A(H1N1) viruses and is expected to be effective against the 1918 H1N1 virus.

How did people survive the Spanish flu pandemic? ›

But how did the deadliest pandemic ever recorded come to an end? Over time, those who contracted the virus developed an immunity to the novel strand of influenza, and life returned to normal by the early 1920s, according to historians and medical experts.

What developed to protect people's health after the Spanish flu? ›

Developments since the 1918 pandemic include vaccines to help prevent flu, antiviral drugs to treat flu illness, antibiotics to treat secondary bacterial infections such as pneumonia, and a global influenza surveillance system with 114 World Health Organization member states that constantly monitors flu activity.

What was the Spanish flu and how did it impact the war effort? ›

Influenza clogged transportation lines along the battlefront, choked hospitals, killed thousands of soldiers, and rendered many more non-effective. The flu depleted and demoralized troops, and may have diverted military and political leaders from fighting the war to combating disease.

How did they get rid of bodies during the Spanish flu? ›

Five hundred bodies crowded the city morgue, which had a capacity for only 36 corpses. The city scrambled to open six supplementary morgues and placed bodies in cold storage plants. Some Philadelphia residents were unceremoniously tossed into mass graves that had been hollowed out by steam shovels.

What was traumatic about the Spanish flu? ›

The influenza pandemic of 1918 and 1919 was a profoundly traumatic event. It killed some 50 million people and infected up to a third of the world's population. Unlike most flu strains, this one was particularly deadly for young adults between ages 20 and 40, meaning that many children lost one or both parents.

How did the Spanish flu change the economy? ›

During both the pandemics, the economies registered a fall in the per capita GDP. Maddison Project Database (2020), as depicted in Figure 3, suggests that during the influenza pandemic, per capita GDP fell from US$1111 in 1917 to US$968 in 1918. However, in the later years, the per capita GDP began to rise.

How did the Spanish flu affect healthcare? ›

Virus was a relatively new concept in 1918, and when the flu arrived medics were almost helpless. They had no reliable diagnostic test, no effective vaccine, no antiviral drugs and no antibiotics – which might have treated the bacterial complications of the flu that killed most of its victims, in the form of pneumonia.

What helped spread the Spanish flu? ›

In fact, more U.S. soldiers died from the 1918 flu than were killed in battle during the war. Forty percent of the U.S. Navy was hit with the flu, while 36 percent of the Army became ill, and troops moving around the world in crowded ships and trains helped to spread the killer virus.

Was the Spanish flu a weapon? ›

Some of the allies thought of the epidemic as a biological warfare tool of the Germans. Many thought it was a result of the trench warfare, the use of mustard gases and the generated "smoke and fumes" of the war. A national campaign began using the rhetoric of war to fight the new microscopic enemy.

How did Spanish flu affect children? ›

Children born during the 1918 flu were more likely to struggle with health-related issues and poverty throughout their lifetime than those born just before or after. Non-white children faced even greater adversity. No transformative child and family policies emerged from the 1918 flu pandemic.

What effects did the pandemic have on the economy? ›

The pandemic was accompanied by historic drops in output in almost all major economies. U.S. GDP fell by 8.9 percent in the second quarter of 2020 (figure 3-3), the largest single-quarter contraction in more than 70 years (BEA 2021c). Most other major economies fared even worse.


1. The 1918 Spanish Flu—A Conspiracy of Silence | Part 1 of 3
2. The Spanish Flu Was Deadlier Than WWI | History
3. Episode 2: 1918 Flu Pandemic in S.C. | History in a Nutshell
4. BBC- The Spanish Flu: a warning from history
5. How the Coronavirus Pandemic Compares to the Spanish Flu | The New Yorker
(The New Yorker)
6. What happened in the Spanish Flu Epidemic in 1918
(World Economic Forum)
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