I currently have 9 chickens. 4 are a year old and 5 are 3 months old. I plan on getting some more in the future and I was just wondering if you recommend me getting chicks that are unvaccinated. I know this differs but my question is... are chickens over 15 weeks who have not been vaccinated likely to get mareks disease even if there are no younger chicks around? How likely are chickens over 15 weeks to catch mareks, etc... GOD bless. 
