With that high number of young people dying of the flu back then you may say that the host mutated and became less susceptible to the original strain of the flu.

Since SARS-CoV-2 seems to be especially dangerous for people after reproductive age I don‘t expect the same pressure as with flu. It may influence our inverted age pyramid, though. And it may have influence on the number of highly educated people >50 and older people with disposable income. (I belong in this group)