Wwyd? I have two sick chicks and it could very well be Mareks. We don't know yet. They are at the vet right now . All of my flock hangs out together and free ranges so they have been around everyone. We kept them in isolation for 6 weeks and then released them into the flock. Is it safe/smart to bring in new chicks when they haven't been vaccinated for it? And can you vaccinate them even if they are several weeks old? I don't want to give a death sentence to new chickens.