> Someone who gets polio from an oral polio vaccine is vaccinated
Vaccine-derived polio cases are not in the person who got the oral polio vaccine [1].
The vaccine recipients are vaccinated. But they can spread that live, attenuated virus to others. If it keeps spreading--among the unvaccinated or IPV recipients--it can mutate and become dangerous. Eventually, dangerous enough to cause polio.
But only to the unvaccinated. The original vaccine recipient isn't injured. They got the attenuated virus. And nobody vaccinated around them is injured, either. It's solely the unvaccinated around them who got the monster that virus mutated into.
Someone who gets polio from an oral polio vaccine is vaccinated. That's how they got the infection: from vaccination against polio.