I'm getting some chicks from Ideal this week who will have the Marek's vaccine. The rest of my flock has never been treated for it. I heard something in passing that you can't put vaccinated chickens with non-vaccinated, because then the others will catch Marek's from them, but then right after that I heard that that was just a silly old wive's tale. Soo which is true? Will my old flock members be safe or not? If not, could I treat them so everyone can live together without any trouble?