Their concerns are for things that can wipe out barns of commercial birds. Meat birds don't live long enough and egg layers are typically vaccinated iircIt’s weird that they’d test for influenza and other things that kill birds but not Mareks. Should have known better with federal certification, though. I stand corrected.
Vaccinated chicks can get it if they are exposed the first 2 weeks while the vaccine is still working or if they are given the vaccine after the 24 hour window. Properly Vaccinated and quarantined chicks are safeI don’t know if anyone can breed for resistance and I’ve read that even vaccinated chicks can get it. It’s probably a lot like any virus…if the animal (or human) is healthy and has a healthy / robust immune system, the chances of it being fatal is less. Exceptions always exist though.