Mareks is everywhere and the vaccine is designed to lower the percentage in a flock that gets the secondary mareks cancer. That starts at about age 2. If the report did not find tumors, I would not worry too much about mareks. From what I have seen, the more lethal strain of mareks involves chicks dying during the initial infection.
Make sure new flock members are vaccinated. If ordering from a hatchery, it is an add on per chick.
Mine were supposed to be vaccinated. I did lose a chick this year at just two weeks, and they were integrated from the start, since I got them for my broody. Her symptoms were very Marek’s-like, I just was not aware they could get it so young (UC Davis vet working my hen’s case confirmed it can.) But, yeah, since mine are supposed to be vaccinated, I’m a little less freaked out.