There are two polio vaccines - the conventional live-attenuated polio vaccine works really well in developing settings, because it's cheap, multi-dose, and vacc

There are two polio vaccines - the conventional live-attenuated polio vaccine works really well in developing settings, because it's cheap, multi-dose, and vaccinated individuals shed virus, which give people who were previously or un-vaccinated some protection via exposure. But if we ever get down to actually thinking "These are the last 5 cases..." it's entirely possible to use the killed virus formulation used in the U.S. and Europe. Where those cases are is a bigger pain.