alt Hacker NewsWell, it's complicated. As I understand, one of the polio vaccines - the oral one - has an unusual quirk.
The live virus used in it can reproduce and spread in low-vaccination communities. While the vaccine version of it will not cause paralysis, it can and occasionally does mutate back into a pathogenic variant.
So we're sort of maintaining a reservoir of polio, really.
Hopefully though we will slowly wean off the live vaccine. For the most part the live vaccine is only used in developing countries. There are a bunch of factors that make that difficult but i think eventually we will get there.