Canada

Since nobody else is bothering to explain it, there's a very good reason the avian flu vaccine is not used regularly in almost any country. The vaccine makes the chicken likely to survive the flu, but it does nothing to prevent infection. So instead of AF outbreaks being detected and the unfortunate birds culled, you would have entire farms incubating thousands of chickens full of AF virus, creating perfect conditions to mutate and potentially spawn a new strain which may wind up being resistant to the existing vaccine. Meanwhile, those infected chickens will be spreading AF to every wild bird for miles around. It's not a useful tool for prevention, it's our last ditch protection if AF gets completely out of control on a global scale.

There's now numbers showing that the bird flu, real as it is, did not result in a significant dip in egg production in the US. Egg producers increased prices on the news about the bird flu and kept increasing them while it was still going. Cal-Maine, the largest egg producer in the US made record profits during this period and still do. Their profit margin went from around 7% pre-pandemic to 25%.

So while disease protocols differ, that's not what drove these price hikes. Instead it's the same scheme various oligopolies have been pulling since the disruption of the pandemic. Some reasonably sounding cause for price increses circulates in the media, manufactures consent for price hikes with the public, price hikes occur, they keep going for as long as media provides cover, afterwards prices may stabilize at the higher level, people's attention moves elsewhere.

Against some things, yes...but not against avian flu. Canada has a very rigorous system in place to identify, isolate and cull any infected animals before they can spread disease to the rest of the flock. You know...all the regulatory precautions the US is so reluctant to impose on their poultry industry, for the sake of saving money.

We have strict biosecurity protocols that make poultry barns a sort of clean room. Vaccination isn't required, nor desired.

E.g. https://www.ontario.ca/page/biosecurity-recommendations-commercial-poultry-flocks-ontario