Thanks Speckled Hen for posting the reference to Dr. Brown's Marek's article. I too have spoken with him..and he has been helpful to me.... It does answer the OPs question about what age Marek's vacinatioin can be done.
If memory serves it is Turkey Marek's that is used in the vaccine, and that virus gives chickens immunity. Possibly speckled hen has turkeys near the chickens.
Here is a link to an under-construction page on BYC, if you have fournd some facts, articles or management practices that will help the BYC community, please feel free to edit this page and post for others who may be finding out about Marek's
https://www.backyardchickens.com/a/mareks-disease-fact-site
Thanks.
It was great adding to the page for Marek's. I've added stuff with reference. I hope we can make a really good page here, Thanks!
Can I link it in my signature?