I found an article in the Internet about Marek's vaccine that has completely blown my mind. http://www.pbs.org/newshour/updates/tthis-chicken-vaccine-makes-virus-dangerous/ I have been a chicken keeper for almost 5 years and every time I get chicks I have had them vaccinated for Mareks. My first encounter with the virus was about three years ago when one of my ameraucana pullets got ill and died after taking her to the vet. My vet said she had Mareks, I had her tested for it, the results came back positive.I have however always wondered if the test came back positive because she had been vaccinated and obviously had the virus' antibodies. My second encounter was about a month ago when my very young rooster had a bump in his head that came up over night. I thought it was a hematoma but after a week and a half it was still there. I found him dead in the run one afternoon. He had slowed down a bit in the last 2 days of his life but he was still moving around. I did not have him tested for Marek's and he was vaccinated. I cannot say with certainty that he died of Mareks. I would like to hear opinions about this article. It is a complete different approach of what I have read so far and now I wonder if I should continue to vaccinate my chicks ????