I do not vaccinate my chicks against Mareks. There are many misconceptions about the Mareks disease. One is that if you order a day old vaccinated chick it will be immune to the disease. If the vaccinated chick, does not come in contact with feathers, dander, or other chickens that have been exposed to the Mareks vaccine, for a period of 10 to 14 days then it will have acquired amunity against developing the symptoms of the mareks virus. This means keeping them completely seperate from your flock and anywhere your flock have ever been. Not easy to do.
I have been fortunate to not have a case of Mareks at my farm. I realize because the disease is so wide spread that it may not always be the case.
If a bird is vaccinated it does not mean that it won't get Mareks. It means they may not get the worst symptoms of the disease which can kill them. It also will not prevent them from passing the virus on to other chickens as once a bird has Mareks it sheds the virus for life.
It is a decision that you need to make for yourself before you purchase one of my birds. I give a two week from receipt of bird health guarantee.
I have a very good link on the links page to First State Vet Supply that explains the vaccine and the virus very well.