I was watching a mini documentary on natural disasters and one segment focused on the Spanish Flu and the worldwide destruction it caused. The narrator said the majority of deaths-outside of war- were among young and healthy people (between the ages of 15-35). I understand how young children/babies and old people are higher at risk, but I dont understand how this demographic could suffer the most. If any historian could answer this question that'd be great!
This is more of a scientific question since the answer to this is science so you'd be better off asking in one of the science subreddits. I'll give you a quick rundown. The problem with the Spanish Flu was that it caused the immune system to go into overdrive and it was the person's own immune system which killed them. This is known as a Cytokine storm. The young and the old, who generally have weaker immune systems, survived because their immune systems were too weak to kill them.