1918 had another factor: war.
Three million draft call-ups, massive crowding in transportation, training facilities, troop ships, bond rallies, etc.
Plus the stress on resources, including medical that war brings, and in dividing the nations attention and forcing a cold decision: react to epidemic or make war.
I know that well. Hundreds died just a few miles from my doorstep at Camp Dodge, in Iowa. Otherwise healthy young men and women. Oddly, according to one account the guys who had just arrived from Alaska were particularly hard hit.
Also, my Grandma’s cousin Mary went off to France as a nurse, survived the war, and died of the flu at the age of 23 after she had returned home.
http://www.iptv.org/IowaPathways/mypath.cfm?ounid=ob_000279