Of all the horrors of World War I, it wasn't the bombs, bullets, or even the mustard gas that ended up as the greatest killer. In reality, the act of moving that many people around the world turned out to be the most deadly fruit of war. The last year of the war, 1918, saw the most deadly pandemic the world has ever known. With all those millions of soldiers being shipped around the globe, it spread like wildfire. This was the Spanish influenza pandemic. In terms of sheer numbers killed, the Spanish influenza beats out the Black Death as the king of historical epidemics. The statistics of the Spanish flu are just brutal, and the disease touched every corner of the globe. It ranks as one of the worst diseases in history, a reminder of how deadly influenza can really be.
The Spanish influenza pandemic killed people on the scale of the fourth rider of the Apocalypse. It is estimated to have killed between 50 and 100 million people worldwide between 1918 and 1919 alone. To put that into perspective, the four years of WWI only killed 17 million people total. Just in the US, over half a million people were killed by the flu, five times as many Americans as were killed in the war.
The flu infected (but didn't necessarily kill) even more: about 1/3 of the world's population was believed to have been infected by some form of the Spanish flu. That's 500 million people at a time when there were only about 1.5 billion people on the entire planet.
The normal victims of the flu are typically babies and really, really old people - like, spare hip, dinner at 4:00 pm kind of old. When a 50 year old dies of the flu, it's a pretty big deal. And a 25-year-old gym rat might think of the flu as a crummy week or two in bed, but the term "life threatening" wouldn't even come to mind. The Spanish flu turned all that on its head. Young, healthy guys would get home from work one day feeling a little sluggish, and then get carried off in a body bag the next morning. Suffice it to say, that freaked a lot of people out.
Unlike normal flu viruses, Spanish influenza seemed to target those between 20 and 35. The reason for this is that people born after 1889 had no exposure to anything similar to the 1918 virus strain. Those born before that date had some exposure to a similar flu strain; therefore, they had some immunity. That discovery didn't come until 2014, though, so people at the time were left guessing why Johnny-six-pack next door just dropped dead while Aunt Gertrude was still going strong.
Like college basketball champions and the world's supply of corn, the Spanish flu seems to have come from unassuming Kansas. While the state boasts many fine and comfortable establishments, Fort Riley was not one of them. In 1918, the army camp housed 26,000 men and was described as bone-chilling in the winter and sweltering in the summer. Oh yeah, and they burned tons of manure from the many horses and donkeys on the base, so it probably always smelled like a paper mill.
On March 9, conditions at the base got a lot worse. The cook, Albert Gitchell, reported to the infirmary with a bad cold. By noon, there were over 100 soldiers in the infirmary, apparently suffering from the same malady. In total, 1,127 soldiers came down with the flu, 46 of whom died.
The condition spread to other camps but, given that war was declared, the brass kept a tight grip on the information. Besides, an outbreak of illness among a bunch of men closely quartered in less than ideal living conditions was hardly that unusual.
In March of 1918, 84,000 American soldiers were shipped off to Europe. In April, another 118,000 crossed the pond. Along with them, the soldiers brought a chance at victory for the Allied Powers. That, and also the deadly influenza virus.
Imagine that you've been living in a muddy trench for the past three years, dodging bullets, ducking artillery, and chasing off rats. Somehow, you are still alive. Finally, some serious reinforcements are coming in, and things are looking up. Then, out of the blue, you catch the worst flu you could possibly imagine. Before you know it, you are lying on an army cot jammed next to a bunch of fellow flu victims, dying in a state of complete delirium because of your high-grade fever.
In the month of June, 31,000 influenza cases were reported in Great Britain. The virus rapidly spread across enemy lines and beyond into Russia, India, and North Africa. By July, the disease had spread across the Pacific to China, Japan, the Philippines, and New Zealand.