I was told that the mareks vaccine for the older birds did shed some cells at the vaccination site, and that the quarantine period for them was as long as three months. Sorry for the confusion. I did read that for one of the vaccines the birds shed for rest of their lives, but I'd have to back over my research to find which one that was. I know all of this confusion causes a bit of a panic, and I don't want to be the cause of another. That's why I always caution folks to do a great deal of research before vaccination. Unfortunately, like I said before, the facts are very hard to find, and I found many conflicting statements, so it was really hard to know what was the real story. Even my vet had a hard time finding information about them. Based on that difficulty, I decided not to vaccinate until I feel confident I know for sure what the consequences are, both to my own flock as well as others.There is a bit of confusion about the "live" vs. the "dead" vaccines, and I am not an authority on either. I have heard of shedding with mareks, fowl pox, and laryngo vaccines, but again, I don't know which version. There was a question within my club awhile back, and it was very, very difficult to find reliable information about the vaccines on the web, because almost all vaccines are created for the industry, and the shedding is not an issue, since all the birds are in one building anyway. It's only when the birds travel that the shedding can create problems. Even here on BYC it was hard to separate fact from opinion. I will tell you I get most of my information from First State Vet Supply - Doc Brown. As a result of these difficulties, I have chosen not to vaccinate my birds, and take the gamble that others will be aware of the consequences of vaccination. I simply can't find out enough solid information to make me take the leap to do it myself. I'm not going to put someone else's flock at risk because I didn't get enough information. Knock-on-wood, I've been ok so far.
As far as my research has led me, neither the vaccine available to the public nor the ones used at hatcheries can make a chicken shed live chicken Marek's disease. The only live vaccine they are ever given for Marek's is a turkey version of the virus, which cannot become symptomatic in chickens. This misconception has falsely scared many people away from the vaccine for Marek's.
I will need to research fowl pox and laryngo.