Im concerned about 1 of my 4 month old chickens-either injured leg (2 days ago) or possibly mareks. Would it be smart to try and vaccinate the others at this point? Or is it too late? Being new to chickens, I bought day olds from a breeder and a couple older healthy hens from another breeder. I thought you could only vaccinate on Day 1 or 2....I am 5 months into this and it will kill me if I loose all my babies. Trying to figure out if this turns out to be Mareks, where to go from here?