A relative of mine was in the Army when the Spanish Flu hit. The Army brass decided that the best way to keep everyone on the base from getting the flu was to send them all home for a few weeks. They had no idea about the incubation time, and the flu spread everywhere. That relative didn't die, but his brother did and my grandfather nearly did. Spanish flu was notorious for killing the folks who normally would be the most likely to survive an illness. When it hit, you might be dead in a day or two.
The wifes grandmother was a teenager during the Spanish Flu epidemic.
She related it was very bad with people dying almost every day on the street where she lived.