I was just made aware by a breeder that it could be a problem. My two,a ccllb and a pbr, were vaccinated as chicks for mareks and are on medicated chick feed. They're a little more than 3 mos old. The pullet I am looking to introduce to my mini flock is not vaccinated. He told me that mareks only protects by suppressing the symptoms of the disease but mine could still possibly have the disease. If they do, introducing a bird without the vaccine will expose the bird and more than likely kill it. So, my question is when can I vaccinate the newcomer? Can a pullet be vaccinated or is it too late then? I raised my two from chicks so how likely is it they would have even been exposed to mareks? I found some pullets I really would like to purchase (one is a $75 auracana) but I don't want to bring her home to expose her and have her die I don't know of any avian vets in the area either so I'm at a loss here. I wouldn't even know how to administer the vaccine or how long it takes before its working. Hubby is willing to chance it... He's a gambler at heart!!