Also:
Contains this lovely tidbit:
“But since nearly every chicken in agricultural production throughout the world is vaccinated, Marek’s is a relatively minor problem today.”
Complete dependence on the vaccine otherwise a disease that used to be a minor annoyance would be wiping out flocks wholesale.
Your conclusion is incorrect. If the industry is dependent on the vaccine it is because of overcrowding, stress, and the horrid way chickens are kept in mass farming.
And, among other factors, there is exposure. If you are not vaxxed but never exposed, it won’t matter.