My friend bought 15 pullets recently from a private breeder. He was told they were vaccinated against Marecks. Two died and were diagnosed with Marecks (with tumors) or Avian Leukosis. They also had bacterial infections in their lungs that were contagious to humans. The one chicken had a neural tube defect and encephelcole. This means that the skull was split and a tumor was sticking out when the chicken hatched. May of the 15 are roosters. The feed store told me that the breeder is known for having sick birds and is spreading Merecks around the Bay Area in Northern California. Here is the question. I read the rest of the flock will have a chance if I vaccinate with Marecks. It will prevent tumor formation. Others say that if I vaccinate with lowered immunity it will kill the birds. Does anyone know what to do.