Spanish Flu

The Spanish flu pandemic of 1918 infected an estimated 33% of the world’s population. There were no effective treatments and no widespread efforts to prevent the spread. There are some comparisons to the COVID-19 pandemic.


What is the Spanish flu?

The Spanish flu was the name given to a form of influenza (flu) caused by an H1N1 virus that started in some type of bird (avian origin). 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. This amounted to about 33% of the world’s population at the time. In addition, the Spanish flu killed about 50 million people. About 675,000 of the deaths were in the U.S.

Just like the flu we get today, the Spanish flu was particularly harmful to infants under age 5 and people over the age of 65. One thing that was different about the Spanish flu was that it also killed a large number of healthy adults, aged 20 to 40 years.


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Symptoms and Causes

What caused the Spanish flu?

The Spanish flu was a type A form of influenza virus that started in a bird host (bird flu), as discovered during later research. At some point, it was transmitted to mammals.

Influenza types A and B are responsible for seasonal epidemics of flu (outbreaks in communities). Type A forms of influenza are the only ones known so far to cause pandemics (outbreaks worldwide).

What were the symptoms of the Spanish flu?

Symptoms of the Spanish flu were similar to the symptoms we all watch out for during flu season. However, Spanish flu symptoms were more severe and included:


What were the complications of the Spanish flu?

As a result of having the Spanish flu, many people died from pneumonia and other respiratory illnesses. Some people died on the same day that they became ill.

Diagnosis and Tests

How was Spanish flu diagnosed?

There were no tests to diagnose the Spanish flu. Healthcare providers had to rely on reported signs and symptoms.


Management and Treatment

How was Spanish flu treated?

There were no medications effective against Spanish flu or antibiotics to treat the infections that people got as complications of the flu. There were also no machines to provide mechanical ventilation and no intensive care units.


How was the Spanish flu prevented?

There were no nationwide prevention methods in place against the Spanish flu. Some communities did put into place prevention methods that may look familiar to us today. The measures included:

  • Isolation, or staying away from crowds of people. This included closing places like schools and gyms.
  • Washing your hands completely and often.
  • Wearing protection like masks and gloves.
  • Not touching outside items like library books.
  • Not spitting in public.

Additional Common Questions

Why was the disease behind the 1918-1919 pandemic called the Spanish flu?

Spain was unlikely to be the source of the Spanish flu. It’s possible that the flu might have begun in the U.S. or France. But Spain was neutral during World War I and didn’t censor its news. Therefore, Spanish news sources reported the results of the devastating disease that was sickening and killing people. People all over the world were getting sick and dying, but countries involved in World War I were censoring the news.

What made the Spanish flu so deadly?

Some of the reasons why the Spanish flu killed so many people include:

  • The lack of effective treatment, due in part to the unknown cause at the time.
  • The cramped living arrangements of animals and people, especially the military, during World War I.
  • The lack of healthcare providers. A significant percentage of doctors were off fighting in the war.
  • The exceptional ability of the virus to copy itself and infect the lungs. This last feature was found during research into the 1918 virus, using tissue found in people who had died from the Spanish flu.

How long did the Spanish flu pandemic last?

The Spanish flu is said to have lasted from 1918 to 1919, but some sources put the date of the end of the pandemic in 1920.

Does the Spanish flu still exist?

The Spanish flu pandemic is over, but similar influenza viruses are still active.

What are the differences and similarities between the Spanish flu and COVID-19?

The Spanish flu and COVID-19 viruses aren’t the same. They are similar in that they're both respiratory viruses spread through breathing in infected respiratory droplets. In addition, they both did and can cause acute respiratory distress syndrome (ARDS). They are also similar in the ways that governments tried to fight them:

  • Avoiding delays in diagnosis.
  • Efforts to develop medication.
  • Isolation/lockdown.
  • Protective clothing like masks and gloves.
  • Hygiene practices like thorough hand washing.

COVID-19 has killed as many people in the U.S. as the Spanish flu did. But the population of the U.S. is now three times more than it was in 1918, so Spanish flu killed a larger percentage of Americans than COVID-19 has to date. If we look at the cause of death, people who had Spanish flu generally died from pneumonia and people who had COVID-19 died from multiple organ failure. Even in the case of people who developed ARDS after infection by each virus, the fatality rate was 100% for Spanish flu, as compared to 53.4% for COVID-19 because there were no treatments for infected individuals. The Spanish flu was also more deadly to healthy younger people, while COVID-19 has mostly affected people who are 65 years or older who have other diseases until the delta variant, which is infecting younger and healthier people more than prior COVID-19 variants.

A note from Cleveland Clinic

The recent COVID-19 pandemic brought many comparisons to the Spanish flu pandemic of 1918. In some ways the comparison was fair. It’s important that we apply the lessons that we learned from both of these public health crises to help us prevent another one.

Medically Reviewed

Last reviewed on 09/21/2021.

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