I lost one!

[Killerbunny]

The problem with vaccination is it sheds. This then exposes any non-vaccinated birds to the virus. vaccines only work for some of the strains and there are at least 6. IMO I don't vaccinate for this and hopefully have resistant birds.
https://www.merckvetmanual.com/poultry/ ... in-poultry
http://www.merial.ca/en/poultry/product ... -sb-1.aspx
Vaccination is advancing all the time and currently there are discussions ongoing as to whether it could make the disease more virulent.
https://www.ncbi.nlm.nih.gov/pubmed/15757475
Hope this helps.

[Happy]

I've read a lot on the vac and I think there's still too many questions over answers where that's concerned. I'm asking more about what happens if you get it. I don't bring in adult birds but there's been many, many times I've wanted to. Is an adult bird that was exposed but resistant able to spread the disease?

[Ontario Chick]

Ugh, sorry to hear that. I hope you've seen the end of it for a bit.

Must be in the air or something, she hasn't brought in chickens either.

Actually, it IS in the air. Specifically, it's on feather/skin dust, and that stuff spreads far and wide. Wild birds get Mareks all the time, and are quickly caught by predators, limiting the spread, but can shed before there are symptoms.
Keeping resistant birds, and quickly culling suspected infected ones, is the best way to go in my opinion. Nursing sick birds, or vaccinating for Marek's, just insures that live virus sticks around much longer than it otherwise would

Jan as usual covered thing very well.
If you go along with what is now general opinion along veterinary professionals, that actually most flocks have Mareks in some form or another and only the ones that don't have resistance will develop symptoms that will most likely kill them, then you are on the right track. The dormant virus can survive in a flock and not rear it's ugly head until there is some stress in the flock (may be brought on by newly introduced birds and then we mistakenly assume it was an infection introduced by them) and then all hell breaks loose.
Assuming that the most birds if they succumb will be 3-5 month old pullets and the signs are pretty obvious, I don't count my pullets until they are 5 month old, although I haven't seen Marek's in my flock in a decade.
This is much easier done in a larger closed flock like mine, a bit more difficult to deal with in a flock of few birds where new birds are introduced on regular bases.