We know that the First World War ended in November 1918. No one in the War knew that, however. Russia was imploding in the east then. On the western front, Germany mounted yet another offensive, only to halt when losing too many of its young soldiers to a malady. America and its European allies, likewise, suffered heavily from the affliction. Everyone blamed the hellish trench warfare, of course. Truth be told, the silent killer was an influenza cutting through the world like a hot knife through butter. The 1918 flu pandemic possibly caused 100 million deaths worldwide, far worse than the Black Death of the Middle Ages. Worst of all, half of those killed were young men and women. Their robust immune systems did them in, ironically. Clinically, they were cytokine storm victims. (Cytokines are lethal weapons courtesy of white blood cells. They are supposed to seek and destroy -- in this case -- the flu virus infecting the lungs. But waves after waves of cytokines can also bring collateral damage to the pulmonary capillaries.)
A healthy young person can easily activate a super-strong immune response. That's good news. The bad news is that such an immune response is effectively a super-massive surge of cytokines otherwise known as a cytokine storm, which is a super-overkill. As a result, the lungs are overwhelmed with dead cellular and viral bodies, fluid, debris, you name it. The lungs are thus stressed out, so much so that they simply collapse. There is a medical term for this scenario: Acute Respiratory Distress Syndrome (ARDS), which severely if not fatally disrupts the supply chain of oxygen and blood. Where the 1918 flu was concerned, an immune system's runaway success could be a youth's agonizing demise.
The 1918 flu (H1N1 influenza A virus) is still widely and incorrectly called the Spanish Flu on social media. Actually, its first outbreak took place in Kansas, USA. WWI troop movements gave the flu virus a global passport.
By the way, there is a mention of the deadly 1918 flu near the end of Kawabata Yasunari's novella, "The Dancing Girl of Izu."
