[summa_tech]

Well, 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.

[bawolff]

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.

[cubefox]

Source?

[ksenzee]

Not OP, but this is fairly common knowledge. Here's a reliable source - search the page for VAPP: https://www.chop.edu/vaccine-education-center/vaccine-detail...

[cubefox]

Thanks.