I practice the same here never lost a bird due to fowl pox either, Mareks yes but still think the practice of survival of the fittest is best here for that. The strong with good immune systems should handle this alright, the ones that would get it usually could contract anything else too in my findings, natural selection at its best.There is no shedding of virus from the Fowl Pox vaccine. I have read some studies that show Mareks does not shed a virus either. Mareks is everywhere and chick are exposed to it as soon as they hatch. The recommended method for inoculating for it is to inject the vaccine into the egg prior to hatching.
I do not raise mine Organic but am feeding them GMO Free, non soy, non corn feed. I have never vaccinated for anything but have used wormers and Corid for Coccidiosis.
People still want Free Range and etc. The eggs I sell are in great demand. I only process for myself so it is not a big problem there.
Jeff