Mareks is virtually every where and we are ALL at risk for this disease. As I understand it there is NO place that safe. Its a race to get the vaccine and antibodies produced BEFORE exposure. You would want to vaccinate at a day old and actually keep the vaccinated bird inside away from exposure (exposure would be outside and adult birds) until the chick has had ample time to develop the antibodies and immunity. I have read this is at the very LEAST 14 days after vaccine some say even longer. Once ample time is given for antibodies to be produced then they can go outside. Most think they can vaccinate then put the chick outside and this is a mistake.. they CAN catch the disease if ample time was not given to allow antobodies to form before exposure. This is why its likely to late for older birds to be vaccinated. It will not hurt them to vaccinate but likely it will not protect them either because if they have been outside and around adult birds the chances are very high that they Are already exposed. Being exposed the vaccine will not help at that point. Its really a race to get the antibodies and immunity BEFORE the chick becomes exposed. Because Mareks is litterly every where you would want to vaccinate and give the time for antibodies production before exposure.