20-40 year old who had spent the previous four years getting their immune systems wrecked by the World War, and the horrible conditions remaining there after.
That’s NOT how it worked. The Spanish Flu caused an over-reaction by healthy immune systems that damaged healthy tissue / cells. People with weak immune systems did better.
Come to think of it, we have all this irresponsible talk of this one being some sort of escaped bioweapon. If I was developing a bioweapon, I’d want it to target the bulk of military age people, and it’d be a LOT more deadly than what we are seeing so far.