I feel the need to clear up some incorrect information here, as some common misconceptions have popped up. First, vaccines are *not* responsible for the majority of chick deaths. Second, coccidiosis is caused by a protozoan, (a parasite), not a bacteria (cleanliness is still a really good idea though). And third, it is simply not true that once you vaccinate for Mareks you always have to vaccinate.
The Mareks vaccine is a live culture of a related strain of virus which is harmless to chickens but does confer effective immunity to the virulent strains of Mareks. It won't stop them from getting infected but it will stop them from getting sick. Any chicken, whether vaccinated or not, can pick up, harbour and transmit the Mareks virus. The difference is that most unvaccinated chickens will develop debilitating and usually fatal symptoms (tumors, paralysis) and the vaccinated ones will most often be asymptomatic. In other words, if your birds have been vaccinated for Mareks you could have the disease-causing virus in your flock but not know it. Some people keep a few turkeys around because they can harbour a non-virulent strain of Mareks, and exposure to it effectively confers immunity on the youngsters the same way the vaccine does.
I vaccinate for Mareks because after reading that there was no need to vaccinate a small backyard flock, I bought 30 day old chicks and a few months later lost all but 4 of them to the disease. I was told by a poultry veterinarian that Mareks is everywhere nowadays and it's no longer realistic to expect backyard flocks to be out of harm's way. By the way, you can in fact vaccinate older chicks and grown chickens for Mareks (the dosage is the same as for the babies). It won't reverse the course of the disease but will stop new symptoms from developing. The idea behind vaccinating them at one day of age is to allow them to mount an immune response to the vaccine strain before they're exposed to the real thing; otherwise it's a race between the two viruses.
pls help me
