This is the best thread I have found:
1. A vaccinated chick is not a carrier of Mareks.
2. Yes, you can raise vaccinated and non-vaccinated birds together. It takes 10 days for vaccine to take effect, and during this time the chick should be quarantined to protect from exposure of Mareks.
3. Your brooder is fine to use again. It should always be cleaned and sanitized between uses.
Here is a copy of the "Doctor's Orders," from the Delaware Club newsletter. Dr. Julie is our vet.
Do you recommend vaccinating the flock? If so, which ones and at what ages?
Poultry vaccines are, generally speaking, a better tool for managing disease that is already present in a flock than they are at preventing disease from getting into the flock. The best way to prevent disease from entering a flock is through good biosecurity, which we can talk about in more detail another time.
One drawback to the use of vaccines in small flocks is the way that they are packaged and sold. Because most poultry vaccine is used by large commercial producers, it is packaged in hundreds or thousands of doses, which is not cost-effective or convenient for vaccinating small numbers of birds.
For these two reasons, I emphasize biosecurity and good management practices over routine vaccination for backyard flock owners, with one exception Mareks disease vaccine.
Mareks disease is caused by a virus, and it is a very common, highly contagious disease of chickens worldwide. Apparently healthy, but infected birds can carry and shed the virus their entire lives. The virus is spread in feather dander and transmitted by inhalation. The infection can cause tumors, paralysis, and suppress the immune system of chickens that are usually older than three months. When Mareks disease gets into a previously uninfected or unvaccinated flock, an epidemic can occur, killing up to 80% of the chickens. Once an infected bird enters a farm, the virus is usually there to stay, unless all of the birds are the removed, and the environment is decontaminated.
Before Mareks disease vaccine was introduced in the 1970s, the disease had a major negative impact on U.S. poultry farms. Unfortunately, the disease still causes a lot of unnecessary suffering and death in backyard flocks whose owners arent aware of the nature of the problem or the availability of a vaccine. Mareks disease vaccine does not prevent chickens from becoming infected with the virus, but it does reduce the amount of virus transmitted by infected birds, and it does a good job of preventing birds from developing illness.
Mareks disease vaccine is given to chicks prior to hatching (in-ovo) or to day-old chicks. If you purchase day-old chicks from hatcheries, I highly recommend that you ask the hatchery to vaccinate them for you before theyre shipped. Most will do this for a small charge. If you hatch your own chicks, you can purchase and administer the vaccine yourself; it is not difficult. It is frustrating that the vaccine usually comes in 1,000 dose vials and must be used on the day its mixed; that means that those of us who hatch a small number of birds will toss out a lot of unused vaccine. At about $20.00 per 1,000 dose vial, youll have to decide if it is cost-effective for you. One option would be to coordinate your hatches with other flock owners so that you can share the vial and share the cost.
Other vaccines for fowl pox and a variety of poultry respiratory diseases are available, but I believe that these vaccines should be used only if a flock is experiencing a problem and a specific diagnosis has been made. Your veterinarian (if you can find one to treat poultry) or your state veterinary laboratory can help you with testing for flock problems. The most information can be gained from necropsies (post-mortems) of affected birds immediately after death.