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-benef

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.