1914-1918 was a dangerous time to be a young adult. The Great War had claimed the lives of over 17 million people and left another 20 million wounded. Over 116,000 Americans lost their lives in the war alone. Yet, as the First World War drew to a close, a far deadlier world-encompassing threat arose – the H1N1 influenza virus.

Unlike the average flu outbreak, which predominantly kills very young, very old, or unhealthy individuals, the 1918 flu pandemic primarily killed healthy young adults. Drafted men who had survived the trenches were now at war with an invisible enemy. Women, who had served in combat-restricted military roles, were now battling an equal opportunity killer. By 1919, 50 to 100 million people worldwide – three to five percent of Earth’s population – had died from the flu, making the H1N1 pandemic more than twice as deadly as WWI. (The outbreak may have even claimed more lives than WWI and WWII combined.)

One of the contributing factors during the pandemic was that doctors had limited treatment and prevention methods. (A flu vaccine would not be developed until 1945.) In fact, it is still a mystery why cases of H1N1 subsided at all in 1919, although a popular theory is that the virus evolved into a less deadly strain. (Pathogenic viruses are known to do this overtime as the population of their hosts drop.)

Although the 1918 flu pandemic was one of the deadliest natural disasters in the history of mankind, it has largely faded from the forefront of American’s minds. Modern medicine has advanced to such a point that many of us do not fear getting sick, certainly not to the degree someone living in the early 1900s would. And though the media is quick to report the latest “epidemic” sweeping the nation, no viral outbreak in recent years has even come close to rivaling the horror of the 1918 flu.