Yes I do. The vaccine only hides the symptoms it does not prevent your birds from getting it. Your older birds might be ok, and based on the age of the birds you’ve lost I’m thinking Marek’s is the culprit. You can’t be sure without necropsy though as you know.
No bloody stools and you’ve had a fecal float test done for worms?
Regardless, a good plan of action is to to scrub out your coops with dish soap, let them dry and then spray with Virkon S. You’ll need to remove the litter and replace, clean the nest boxes, etc.
Don’t beat yourself up over it. The disease is shed in their dander and can blow in on the wind with dust, be carried in by wild birds or rodents, etc. Your best course of action is to immediately put down anyone exhibiting symptoms and breed from those that are exhibiting resistance. Also clean and sanitize before adding chicks.
