They stay on my property, but since it travels through feather dander that doesn't really matter on a windy day. My birds contracted it from somewhere, and it wasn't from the breeder, and I don't go to shows or have friends that own chickens. As I said before, the closest chickens to me are about 1/4 mile.
Vaccinating a chick at one day of age will not keep it from getting the disease, nor will it keep it from spreading the disease if it does contract it. So we are only fooling ourselves thinking that a non-syptomatic bird is disease free. They can be carrying it anywhere it or there feather dust goes. I have read that we should all just assume that our birds are infected. Vaccinating lets you enjoy "healthy" birds, so you may be spreading it and not knowing, and since there is no test on live birds where does that leave all of us? I think that leaves us having a false sense of security. It may be that infected birds are being sold and traded and no one knows about it until they infect an unvaccinated flock. And if it takes 6 weeks for symptoms to appear then a 30 day quarantine isn't long enough, and if they are on your property and in quarantine that is too close.
I haven't had any sick birds since I vaccinated my flock, it has been about 6 weeks since I did that. But I am not thinking that they are all disease free.
And why would I burn them if I did cull them? I'm sorry, but that is going a little too far. Burials work just as well. This is not mad cow or hoof and mouth diesease we are dealing with. It isn't even a reportable diesease.
I also have time, sweat, and money invested in my flock. Unless I want to get out of chickens completly I have to deal with the hand I have been dealt. I can't afford to destroy my coop and build a new one. My chickens range with my goats and I don't have the rest of my property fenced so they have to stay where they are.
I may or may not sell, trade, or give away my birds. And they may or may not be infected. I think that those breeders that sell vaccinated chickens can be spreading the disease the same as I may. At least I will tell people the history of my flock and not just "assume" they are disease free because they have been vaccinated.