Introduce 5 week old chicks to adults exposed to Mareks?

[happima]

Last September, I purchased my first four chicks. At five weeks of age, my naked neck died - did necropsy and turns out she died of Mareks.

My remaining three hens have not shown any Marek's symptoms and are now healthy egglaying adults.

I've been thinking about expanding the flock. Found some 5 week old chicks who have all been vaccinated. Was planning on getting them and introducing into flock next week.

I've read mixed info on this - my vet (dog vet) gave me information that indicated I should have a closed flock and not introduce any new chickens into the mix until all my current hens have died and coop has been disinfected. Others seem to think that as long as I wait until chicks are old enough for vaccine to take affect, flock should be fine.

I'm getting cold feet now. I have a healthy flock of three hens and maybe I should just enjoy. Mareks is no fun. Don't want to let that genie out of the bottle on this flock again. Should I just count my blessings and stay put with three hens?

Would love to hear your experience on this.

Thanks,
Jennifer