If you’ve ever had the flu, you know how awful it can be. You suffer from a fever, your nose is running, and your entire body aches. Some are fortunate to be seemingly immune to the virus, while others are constantly fighting it off during its yearly outbreak. Thankfully, modern vaccines and smart precautionary measures go a long way to staying healthy. There was a time when people didn’t have the medical knowledge we have today. It led to a devasting pandemic at the turn of the 20th century that wiped out millions of people.

The beginning of the deadliest flu ever

As World War I came to a close, there were reports of the flu in an American military base. At the same time, there were thousands of troops and casualties being treated at a hospital camp in France. Overcrowding and less-than-ideal sanitary conditions played an important role in the deadly outbreak.

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Modern researchers later discovered that the origin of the virus may have been from Spain, China, or either Kansas or Boston in the United States. While the exact origin may never be known, one thing is certain: this particular strain would eventually kill more people than the war itself.

The outbreak

The close quarters in military camps around the world were the perfect breeding grounds for the virus to mutate and spread quickly. Transmitted through coughs and sneezes, the now-deadly virus led to huge numbers of infections and, ultimately, casualties.

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Known as the Spanish Flu, the 1918 influenza pandemic led to worldwide devastation and affected more people than the Great War itself.

Death by the millions

The fast-moving virus made its way around the globe and turned into a full-blown pandemic. It rivaled the infamous Black Plague of the Middle Ages in terms of global suffering and death. It’s estimated to have killed 50 to 100 million people.

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Researchers estimate that 10 to 20 percent of those infected died, with nearly half of the casualties aged 20–40 years old. Within a year, the virus had apparently mutated into a less deadly strain and deaths dropped to nearly nothing. But not before the pandemic had wiped out nearly five percent of the entire world’s population.