Info on the Spanish Flu I've found online indicates between Spring and Fall 1918 the virus had mutated and had become even more deadly. It was particularly more so for the young. The following was found on the link provided in my earlier post:
Influenza jumped outside the camps and went raging through the civilian population. Because of the way the virus worked it was particularly frightening because it killed young men and women. Normally the flu killed the old and the very young. In 1918, the flu was killing young able-bodied Soldiers.
One of those Soldiers was Pvt. James Down who entered the Camp Upton hospital on Long Island Sept. 23 and died Sept 26. An Army pathologist clipped a piece of James Down's lung, preserved it in wax, and sent it to the Army Medical Museum.
In 1999 that section of Pvt. Down's lung helped doctors at the Armed Forces Institute of Pathology determine what made the 1918 virus so deadly. Researchers in 2007 theorized that the 1918 flu forces victim's over-stimulated immune system to kill the patient as it tries to fight off the virus.
The old Camp Upton referenced in the link is about 20 minutes from my home. Now it is known as Brookhaven National Lab. Every once in a while they find unexploded ordinance on the grounds.https://www.bnl.gov/about/history/campupton.php