The Spanish flu was Sept to Feb, and then it was done and did not come back in any appreciable way.
So that is different than COVID, which is ending in May.
The second waves in the Spanish Flu happened while still in Flu season.
Note the average duration of social interventions in chart above, Seems like WE WENT A BIT BAT SHIT CRAZY THIS TIME!
These curves from the Spanish Flu clearly show an important pattern. Cities that reacted quickly, and then released people from lockdown, quickly, and then, when needed, locked down again, had by far the lowest death rates.
This chart shows that early response is the most important, not the length of lockdown.