Actually, it is a type of flu that causes a “cytokine storm” so that those with the strongest immune systems die the fastest- in 1918, the young and healthy got sick and died in a day. Not that those with compromised immune systems fare much better. But I read one study that anti-arthritis drugs (which suppress the immune system) showed some good effect
history
http://www.riskinstitute.org/peri/images/file/Lessons_from_1918_PartI.pdf