The Spanish flu had a smaller outbreak in the Spring and came back with a vengeance the following Fall, so hold that thought.

https://www.history.com/news/spanish-flu-second-wave-resurge...

Well, sure, but the “Spanish” flu (only called that because Spain is the first country severely hit that didn't lie and cover it up because of WWI) was accelerated by both the physical conditions created by WWI and the fact that covering it up to avoid revealing weakness to wartime opponents hampered response in many early-hit countries and obstructed information flow.

It's also nowhere near the HIV/AIDS global epidemic in likely total impact, but it's a lot more acute in it's impact than HIV/AIDS.

I disagree. It's simply too early to make that determination.

The Spanish Flu had a estimated infection fatality ratio of >2.5% (https://wwwnc.cdc.gov/eid/article/12/1/05-0979_article). As another commenter pointed out, the COVID-19 IFR is 0.9% in NYC. The difference between 2.5% and 0.9% is only 2.8x. However the IFR is not only underestimated due to the lag between case detection and death, but it's also probably a lot worse in many other parts of the world (third world countries, etc). So it's possible the difference is only 2-fold, which would make both pandemics relatively comparable.

Or as bad as the 1957-8 "Asian Flu" that most people haven't even heard of.

Hard to compare directly against the Spanish Flu as medicine has had 100 years of progress, but assuming you are talking about overall impact, agreed.