Isn't the vaccine the turkey herpes virus?
Edited to add:
Chickens are the most important natural host for Marek's disease virus (MDV), a highly cell-associated but readily transmitted alphaherpesvirus with lymphotropic properties of gammaherpesviruses. Quail can be naturally infected, and...
"While the vaccine will prevent birds from experiencing symptoms and greatly diminish the spread of the disease, a Marek’s Disease vaccination cannot completely prevent infection."
Source
To suggest that the vaccine makes them sick sounds like another conspiracy theory.