can adult chickens be vaccinated for marek's?

Marek's usually hits before or at around 5months of age. If you're worried about a five year old dying of Marek's - don't, I'd be more worried about him dying of old age

The thing is, you can vaccinate older birds, but the vaccination will have no effect if they've been exposed at all to the actual virus. Because it is so highly contagious and can be carried in the air from a few miles away, we kind of have to assume all our birds are exposed at some point.

Please DON'T vaccinate for Marek's. It's rare for small flock owners to have problems with it, usually only large commercial meat vacilities and what not vaccinate. Marek's is a live vaccine, so the chicks vaccinated will be immune, but then they can pass it on to non-vaccinated birds. Scary that hatcheries don't mention this. Unless everything I've read has been garbage. Haha. Either way it makes me nervous to think about.

This is in stark contrast to what our avian vet says.  He sees Marek's all the time in small flocks and he highly recommends that you get chicks that have been vaccinated (not sure if it is climate dependent -we are in Northern CA).  Second, although it is a live vaccine it does NOT make your bird a carrier that can infect other birds (at least not a normal reaction).    As with anything, do your own research but thought I'd share what my vet said, which on many other occasions goes against what I read on BYC.

Yeah, who knows. Trial and error always seems to be most accurate when it comes to poultry, everyone will tell you something different. Haha.

Actually, no. Read the label on the Marek's vaccine - it tells you what species and strain is used in the vaccine, it's not the same as what actually causes what we know as Marek's.

And every vet that I've talked to so far (Oregon) has highly recommended vaccinating young birds. It's a vaccine with low side effects, highly tested and effective. But again, I've been told anything over 5-6months old is probably not going to gain anything from the vaccine, but you can try if you're feeling paranoid.

Isn't that the truth, we all are informed and or learn something different and here goes lol! My vet informed me that it is worthless to vaccinate any chicken that is over a few days old since the vaccine will serve no purpose as they get older. He also stated as mentioned above that Mareks is highly contagious and can be caught from many miles away, air born since it comes from the dander of a chicken. I personally would not waste my time nor funds and I must laugh since I was concerned in the beginning also, same as you are now until after speaking with my vet in detail about this deadly disease. Do your research, Mercks Veterinary Manuel is great for information on diseases.

Btw, any flocks can get it, large or small!

Vets will recommend you vaccinate for everything under the sun. I personally think that too much babying doesn't let them build a strong immune system, so when something comes along, they quickly get sick. Just a personal opinion from my experience. I've raised poultry since I was 7 (12 years), and have NEVER had problems with disease. Then again, my birds all free range, and their shelter is an entire barn that was intended for horses. Lol. So they're far from cramped and the bedding will stay clean and fresh for a LONG time.