Years ago I read about the 1919 influenza pandemic that reportedly began in Europe and killed twice as many as World War One deaths in the Smithsonian magazine. Surprisingly it has been forgotten until brought up again recently after Covid-19 came out. In response to that article there were people who mentioned the bad sanitation of hospitals of that time (a problem today), and I noticed that literature from that era that I've seen (including The Great Gatsby) that I've seen fails to mention it.
I wonder how it must have been for both the troops and the civilians in Europe, unless there had been other pandemics just as bad in that era.
For more on the 1918-19 pandemic see on youtube: National WW I museum and memorial has 3 long and 1 five minute presentations on this topic there are also other presentations on this on youtube. Also this site has presentations on what else is happening in the US in 1919 race riots and the 1919 Paris peace confrences.