Kindly, that's not what the article says. This disease is a bit confusing, but there are a few things we know for sure. If you read it carefully it explains what actually happens... vaccinated birds that are exposed to the virus can still spread it but the vaccine, itself, does not spread the virus. The act of vaccinating birds, alone, will not cause the spread of the virus. Vaccinating birds that are then exposed and survive will spread the virus.. the same way unvaccinated birds (that are exposed and survive) will. The studies cited in that link do suggest that vaccinated birds are more likely to spread very virulent copies of the virus due to their higher survival rate (since they were vaccinated) in commercial poultry situations, since the boosted immune systems can drive virus mutation. In essence, the vaccine allows chickens to survive more than ones that are not vaccinated, which is driving the evolution of the virus to be more deadly in commercial poultry farms (it's generally unstudied in small flocks / backyard chickens) due to the sheer numbers of birds and crowded situations. Despite this, even the article itself says that vaccination is still the best option if you read it. I don't mean to debate but I am confident in my research on this aspect of the disease.
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