Yup to what you said.
I truncated my earlier post because I got a call from downstairs that salad, baked chicken, yellow rice was on the table, and strawberries had been cut up for the home made ice cream in the freezer. I believe my priorities are in order.
Reading the study makes it clear that what is happening with these chickens is important to the poultry industry, it's not just a what-if study, it's a "this has happened and we need to find out why" kind of thing.
Anyway, for the benefit of readers who may not have time to read the actual study, in the study, the author mentions what we said, that the increased virulence example that he had discovered for this virus, Marek's virus, had not been seen in human hosts for human diseases.
From the article:
"The imperfect-vaccine hypothesis attracted controversy [11–14], not least because human vaccines have apparently not caused an increase in the virulence of their target pathogens"
Furthermore, the author says:
"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. Clearly, many potentially relevant ecological pressures on virulence have changed with the intensification of the poultry industry."
The study also discusses similar phenomena that occurred naturally when exposed survivors in the wild harbored an increasedly virulent pathogen due to their acquired partial immunity after exposure.
What I think is interesting is that the increased virulence of Marbek's is only found relative to unvaccinated chickens. The vaccinated chickens do not experience the increased virulence.
If there is a lesson in this for human vaccines, it is that when we vaccinate, we need to vaccinate as much of the population as is possible, and that you really do not want to be the unvaccinated ones if an analogue does appear in the human population.
Anyway, this actual study is interesting, and I don't see any problems with the way it was executed or written. As is so often the case, the problem comes from people extrapolating from a study things that are not found in the study.