Unlike with covid, we know how to make flu vaccines on a large scale. Is there a reason why we couldn’t also preemptively vaccinate against H5N1 during regular seasonal vaccination campaigns?
I don't think there's anything in particular that stops us from routinely adding a H5N1 strain into the current flu vaccines. It's just a question of cost-benefit. And as the sibling post notes, getting an avian flu into human form right now is definitely more involved. I imagine if we started using mRNA influenza vaccines, that might change the relative cost.
I suspect with the apparent extinction of the B/Yamagata line, that'd free up a slot in the quadravalent vaccine.
https://www.cdc.gov/flu/avianflu/candidate-vaccine-virus.htm