Still don't see it: Their last line: "Vaccination for Marek’s is also not a guarantee that the chicken will not get Marek’s disease but has been a very effective vaccination. Currently, we use an MD/RISPENS vaccine."
If you're talking about the PBS article they linked, that is not Cackle Hatchery's article nor words; it's a PBS News article.
And their last paragraph: “Even if this evolution happens, you don’t want to be an unvaccinated chicken,” Read said. “Food chain security and everything rests on vaccines. They are the most successful and cheapest public health interventions that we’ve ever had. We just need to consider the evolutionary consequences of these ones with leaky transmission.”