Not a stupid question at all, Cathy! Apparently there is a vaccine available for the avian flu virus, but like other influenzas, the avian flu mutates rapidly so would have to be repeated often to maintain immunity- not sure how effective it would be either. I had to look up the question because I didn't know either, and linked (I hope) is a good article from the Science publication that discusses the vaccine and the pros and cons ( including availability) of vaccinating poultry.

https://www.science.org/content/article/bird-shots-vaccinating-poultry-best-defense-deadly-bird-flu