If your chicken had Marek's, then the rest of your chickens likely do/did too. They're vaccinated, so it's hiding their symptoms. But that doesn't mean they're not spreading it rapid fire. It's a leaky vaccine that causes shedding. I'm pretty certain Marek's is everywhere, it's just that most people vaccinate and are lucky enough not to notice. My vet seems to be of the opinion that vaccinated birds only shed once they've come in to contact with the live virus and have to fight it.
I have had a suspected Marek's case in my flock too. With a vaccinated bird. I plan on letting one of my chickens hatch a clutch of eggs and not vaccinating them, and seeing what happens. I've read a lot about breeding for resistance and live around a lot of Amish that don't vaccinate their birds and have very robust flocks.
So to answer your question, based on what I've read and my vet has told me, your vaccinated chickens will likely spread Marek's if they've been exposed to it.
I have had a suspected Marek's case in my flock too. With a vaccinated bird. I plan on letting one of my chickens hatch a clutch of eggs and not vaccinating them, and seeing what happens. I've read a lot about breeding for resistance and live around a lot of Amish that don't vaccinate their birds and have very robust flocks.
So to answer your question, based on what I've read and my vet has told me, your vaccinated chickens will likely spread Marek's if they've been exposed to it.
