Why the Second Wave of the 1918 Spanish Flu Was So Deadly

The first strain of the Spanish Flu wasn’t particularly deadly. Then it came back in the fall with a vengeance.

1. Virus Killed the Young, Old and In-Between (it mutated): Reported cases of Spanish flu dropped off over the summer of 1918, and there was hope at the beginning of August that the virus had run its course. In retrospect, it was only the calm before the storm. Somewhere in Europe, a mutated strain of the Spanish flu virus had emerged that had the power to kill a perfectly healthy young man or woman within 24 hours of showing the first signs of infection. There were two, deadlier waves that followed...