[BobbyJo]

What's mysterious about the flu disappearing? The precautions taken to reduce COVID were extremely effective against influenza. Given that it was much more broadly circulating, and therefore a large percentage of the population had antibodies to dominant strains (more than COVID even now), one would expect masks and isolation to basically destroy it's spread no?

[lambdaba]

It's also possible that viral disease dynamics are just like that, with one virus dominating at a time (amongst this class of highly contagious respiratory viruses).