Does that reasoning hold up in the face of states like South Dakota or Florida which barely had any covid measures? Would you expect that lightly-enforced, intermittent and barely-present covid measures would drop a state like Florida from millions of flu cases down to a couple hundred at most? And why do we already have 40k flu cases so far this year, when we had only 2k all of last year?

(1) People in red states have still changed their behavior. In particular if people with flu symptoms are staying home instead of going out that can make a big difference.

(2) I bet a lot of flu is spread by people who go to conferences, travel a lot, etc. These activities are greatly curtailed and often happening in places that are taking precautions so that stops it from entering red states.

Does the flu typically spread at home or only outside the house? #2 is an interesting idea. Florida had a record number of visitors last year (118 million), would it be so accurate then to say travel was curtailed there?