This would seem to suggest that it's not a problem with the vaccine but with the level of sanitation. The one big relevant difference here is that in developed

This would seem to suggest that it's not a problem with the vaccine but with the level of sanitation. The one big relevant difference here is that in developed countries we had flush toilets and sewer systems carrying effluent away from the populace, which may not be true in places that still have polio. So OPV could work but doesn't not because it's ineffective but because the polio-rich effluent produced by vaccinated people isn't being carried away from them effectively. So maybe the best way to eradicate polio is to build sewers and septic systems.