Vaccine Derived Polio

Some incidents of only vaccine derived polio outbreaks.

It's been known since the outset that the polio vaccines sometimes gives people polio and that vaccinated people can infect others for up to a year. The rate at which is does this is increasing. Initially it was 1 in 2.5 million, then it became 1 in a million. As of 2018, paralytic polio from vaccines is the dominant type; there are more cases of vaccine derived polio now than of wild polio. In many countries wild polio appears to be extinct yet vaccine derived polio lingers.