I currently have hens from 8 months- over a year..... I do not know if they have been vaccinated for Marek's.... I have chicks as well in the same building that have NOT been vaccinated... I'm worried that it might sweep through my flock (have a sick chick in quarentine now-not sure what is wrong) and would like any of my chicks that hatch out from now on to be vaccinated but im afraid it is too late... how does this work.... If i vaccinate any day olds that hatch from now on, can they infect my flock that i currently have with the disease? Remember no one is currently vaccinated that i know of..... (my chicks for sure) im afraid i have made a big mistake here, I don't want to start my flock over as I have a lot invested and i don't want my older hens and a rooster to get sick... as i said it may be too late but I need to know soon because I have chicks hatching in a week and i need to locate some vaccine if that is the plan for them! Your help is appreciated, i wish I had known about this before I ordered of bought anything but I didn't an no one I know vaccinates so i really had no clue. I just want to be a good mother hen!