> This is what happened with "Marek's disease" Marek's disease in chicken is what the PLOS article is about: MDV = Marek's disease virus. > The vaccine was "l

> This is what happened with "Marek's disease" Marek's disease in chicken is what the PLOS article is about: MDV = Marek's disease virus. > The vaccine was "leaky" and ended up selecting for a more deadly form The researchers of the PLOS article do not claim to know that for certain: "Our data do not demonstrate that vaccination was responsible for the evolution of hyperpathogenic strains of MDV, and we may never know for sure why they evolved in the first place." But this they claim: "But whatever was responsible for the evolution of more virulent strains in the first place (and there may be many causes), our data show that vaccination is sufficient to maintain hyperpathogenic strains in poultry flocks today." https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1002198 https://journals.plos.org/plosbiology/article?id=10.1371/jou...