Illustration by Jared Whalen; National Museum of Health

Flu pandemic of 1918: One hundred years later

This year’s flu season marks the 100-year anniversary of the flu pandemic of 1918. The pandemic was the deadliest in modern history, killing more people than any other illness in recorded history.

Influenza, or the flu, is a virus affecting the respiratory system and is highly contagious. While flu outbreaks happen every year, influenza vaccines and a greater understanding of how the virus spreads help prevent widespread illness. Even with the vaccine, however, a pandemic could occur if a new virus emerges that most people are not immune to and for which a vaccine is not widely available.

Scroll through the charts and text below to learn more about the flu pandemic and the history of influenza over the century.

The 1918 Flu Pandemic, Worldwide
 100,000 infected
 100,000 deaths
 Equivalent deaths in WWI
The 1918 Flu Pandemic was the deadliest outbreak in modern history. One-third of the world’s population – an estimated 500 million people – were infected during the pandemic. The virus was detected in Europe, the United States, and parts of Asia before spreading around the world, including remote Pacific islands and the Arctic. *
An estimated 50 million people died as a result of the pandemic, making it one of the deadliest natural disasters in human history. While most influenza outbreaks disproportionately kill children, the elderly, and those already sick, the 1918 pandemic killed many otherwise healthy adults. *
For comparison, World War 1 resulted in 20 million deaths, less than half as many as from the pandemic. *
In the United States, nearly 29 million people, more than 25 percent of the population, were infected and around 675,000 died. For comparison, 53,402 Americans were killed in combat or went missing in World War 1. *
The first flu vaccine was developed in 1938 by Jonas Salk and Thomas Francis and approved for civilian use in 1946. * The influenza and pneumonia death rate has since seen a steady decline. In 2015, the influenza and pneumonia death rate for all ages was 15.2 per 100,000. *
The CDC estimates the positive impact of influenza vaccination by using a model to estimate the numbers of influenza illnesses, medical visits, and hospitalizations. The CDC also estimates the number of influenza and pneumonia deaths averted by using reports of respiratory and circulatory deaths attributable to influenza. *
The effectiveness of the influenza vaccine ranges widely from both season to season and person to person. * From the CDC website, “At least two factors play an important role in determining the likelihood that flu vaccine will protect a person from flu illness: 1) characteristics of the person being vaccinated (such as their age and health), and 2) the similarity or “match” between the flu viruses the flu vaccine is designed to protect against and the flu viruses spreading in the community.” *
The CDC is unable to precisely count how many people die from the flu each year for reasons including the sheer number of deaths to be counted, the lack of testing and reporting, and the different coding of deaths since influenza-associated deaths are often compounded by other medical issues. * Because of this the CDC gives a range of estimated deaths. *
Even with the influenza vaccine, the flu proves deadly to thousands each year. Grouped with pneumonia, it ranks as the eighth leading cause of death in the United States between diabetes and nephritis. *
To learn more about the influenza vaccine and how to prevent yourself from getting sick, visit the Center for Disease Control’s website.

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