The first strain of the Spanish flu wasn’t particularly deadly. Then it came back in the fall with a vengeance.
The horrific scale of the 1918 Spanish flu pandemic is hard to fathom. The virus infected 500 million people worldwide and killed an estimated 20 million to 50 million victims— that’s more than all of the soldiers and civilians killed during World War I combined.
While the global pandemic lasted for two years, the vast majority of deaths were packed into three especially cruel months in the fall of 1918. Historians now believe that the fatal severity of the Spanish flu’s “second wave” was caused by a mutated virus spread by wartime troop movements.
When the Spanish flu first appeared in early March 1918, it had all the hallmarks of a seasonal flu, albeit a highly contagious and virulent strain. One of the first registered cases was Albert Gitchell, a U.S. Army cook at Camp Funston in Kansas, who was hospitalized with a 104-degree fever. The virus spread quickly through the Army installation, home to 54,000 troops. By the end of the month, 1,100 troops had been hospitalized and 38 had died after developing pneumonia.
As U.S. troops deployed en masse for the war effort in Europe, they carried the Spanish flu with them. Throughout April and May of 1918, the virus spread like wildfire through England, France, Spain and Italy. An estimated three-quarters of the French military was infected in the spring of 1918 and as many as half of British troops. Luckily, the first wave of the virus wasn’t particularly deadly, with symptoms like high fever and malaise usually lasting only three days, and mortality rates were similar to seasonal flu.
Full story at: https://www.history.com/news/spanish-flu-second-wave-resurgence