The live attenuated oral polio vaccine is contagious and has already been widely used in many countries.
"However, this live vaccine is continued to be used worldwide. And while you're doing that, some of that vaccine has gotten out into the world. And it's mutated. It starts circulating again, just like regular polio. But early on, it's just - it's still a vaccine. It's not dangerous. And then slowly, it sort of regains strength. And they're finding they can actually genetically see this - that scientists can actually trace it back directly to the vaccine. And now these vaccine-linked cases are actually causing more cases of paralysis each year than actual traditional - what scientists call wild polio."
https://www.npr.org/2019/11/16/780068006/how-the-oral-polio-...
SIMON: Now, we should underscore, Jason, this is not the version of the vaccine that's given to youngsters in the United States.
BEAUBIEN: Yeah.
SIMON: Why are other countries still using it?
BEAUBIEN: Right. So in the United States and in Europe and other countries like that, it - we're using an injectable vaccine, which is a dead vaccine. It is not a live virus, and it cannot cause polio. So that should not at all be a concern. The issue, however, is that it's an injection that has to be given. It's given four times between the ages of 2 months and 7 years. So just administering it is difficult. And just frankly, there is not enough global stockpile of that vaccine to vaccinate all of the children around the world, you know, four times over the course of their childhood.
A few years ago, there were more polio cases caused by vaccine-derived virus than the wild virus.
That said, it is certainly a shame that the entire world doesn't have access to and capability to administer the inactive vaccine.