I bought two chicks at one month old that I could not vaccinate due to their age (must be done the first day), so I am raising them inside the house for four months because I have lost hens in the coop due to Marek's. The three hens in the coop now were exposed, but did not die and are around 1 1/2 years old. They are on a dirt/pebble floor, though I spray with Vitaoxide a little (a hospital disinfectant) and wash it down about once a week.
Do I need to also rake up the feathers? And how soon can I let them into the yard? Or, into the coop. My thought was another part of the urban yard at two months for short outings, then into an adjacent (touching) coop at 4 months, then join the birds at 6 months (or less).
I do think your best chance is to delay contamination as long as possible. I think what that may do is limit their exposure to the virus enough where antibodies have a chance to grow.