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.
