>Why the young were so vulnerable is seemingly still a mystery.
Originally Posted by
pattern_is_full
One theory you already suggest - debilitation by gassing (or trench life in general).
Another I've seen is that the particular 1918 strain induced immune-system "storms" that themselves caused body damage - a
healthy young immune system could actually be a liability. cf:
https://en.wikipedia.org/wiki/Cytokine_release_syndrome
These weren't really recognized and studied until transplants (and immune reactions to them) became common more than half a century later.
I used to believe the second theory. Which led me to expect that covid-19 didn't involve "cytokine storms" as it hit the oldest hardest. Turns out that
this isn't the case, and "cytokine storms" seem to be heavily involved in cov-19 deaths.
Weeks ago I looked up some Spanish flu references and happened across a plausible-sounding theory that the elderly were protected by lingering immunity
from an earlier flu epidemic. Similar strains hadn't occurred for some time, hence the young didn't have this partial immunity.
Article
https://www.medicalnewstoday.com/articles/276060
Why was 1918 flu pandemic so deadly? Research offers new clue
Paper abstract
https://www.pnas.org/content/111/22/8107.short
Genesis and pathogenesis of the 1918 pandemic H1N1 influenza A virus
Paper pdf
https://www.pnas.org/content/pnas/111/22/8107.full.pdf
Genesis and pathogenesis of the 1918 pandemic H1N1 influenza A virus