From everything I have read and everything I have observed. I just have to wait it out... see who survives and breed resistance in those birds. if I chose to keep chickens anymore. If we lose too many of our favorites I may just euthanized the rest... canning the whole idea of chickens. Additionally I know my chickens will never be safe as Marek's because they already have a compromised immune system.
They worst thing about the form of Marek's they have is you can see it start a day or so ahead of time.... it starts with a slight wobble to their gate, the following day the wobble get worst with them occasionally tripping over themselves or at least that's what it looks like, the 3rd day the bird's left or right foot can no longer open to walk and if you touch the foot and toes they are limp and lifeless, the 4th day the other foot is affected and the side that was affected first has lost more ability, the nerve damage climbs up the birds extremities until it is flat out legs and wings splayed out but able to move its neck but unable to get to food or water,and defecates in place, the final day that I allowed my bird to live he was no longer able to move his neck but was able to blink, react to light and to my voice. I then cull Lyle at this point... soothing voice and such and repeated over and over "Never again".
I wasn't trying to be cruel but I felt I needed to watch the stages to see if it was the same disease affecting the other birds, it is, therefor if we see a staggering, wobbling chicken we know. Now we only let it get to one leg... we feed a wonderful last meal that the chicken thoroughly enjoys, then is brought to a place the others can't see and ...
If these chickens die off ... I may never own another chicken for as long as I live... but I know I will miss them because I really love their antics. I have wanted these chickens since forever, however, prior to this point I was a single mom and nurse. My hours were erratic at best. I only now got to the point where I actually have time for them. I would therefor have to get birds that are immunized. and I don't know if this is helping or hindering the spread of the disease.