Not many, in all honesty. The Spanish flu pandemic came and went in three waves between 1918 and 1920, but the really deadly one--the second--kind of came and went in most areas in a matter of weeks (6 - 8, usually). It was more of a crisis event than a long term "must adapt" sort of event.

Many of the changes were more subtle as a result:

• It became more acceptable to go to hospital (the social preference had been for treatment at home).
• The funerary industry became more professionalized.
• People stopped spitting on the street (we were just having this conversation in another thread, apparently prior to 1918 it was common to spit in public, but this was discouraged widely as it was believed to spread the flu).

But there just weren't a lot of widespread political or social changes -- the pandemic itself was largely forgotten in some areas (the prevailing theory is that it didn't go with the triumphalist narrative that accompanied the end of WWI); there are barely any memorials.

Time will tell how much change COVID has, but I have a feeling that a lot of the changes are going to be in non-medical and non-policy areas: restaurant tables spaced a little further apart (great news to those of us who enjoy elbow room!); innovations in contactless payment; more people working from home (and more businesses willing to consider it); and quite possibly the biggest may well be that the internet is seen as a utility rather than a luxury.

If you are interested in another example that fits /u/Khowaga's summary, I wrote a few words on the impact of the flu in Italy here.