When the Spanish flu first appeared in early March 1918, it had all the hallmarks of a seasonal flu, albeit a highly contagious and virulent strain.
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.
From September through November of 1918, the death rate from the Spanish flu skyrocketed. In the United States alone, 195,000 Americans died from the Spanish flu in just the month of October. And unlike a normal seasonal flu, which mostly claims victims among the very young and very old, the second wave of the Spanish flu exhibited what’s called a “W curve”—high numbers of deaths among the young and old, but also a huge spike in the middle composed of otherwise healthy 25- to 35-year-olds in the prime of their life.
Harris believes that the rapid spread of Spanish flu in the fall of 1918 was at least partially to blame on public health officials unwilling to impose quarantines during wartime.