Because of an active vaccination program in the U.S., there have been no wildtype polio infections acquired within the U.S. since 1979 (see graphic, right). There have been rare importations of wildtype poiio that did not spread, and we have experienced small outbreaks of vaccine-associated polio (cVDPV) involving unvaccinated individuals. These occurrences, though extremely rare, create a situation in which individuals are more likely to acquire paralytic polio from live polio vaccine than from wildtype virus in the U.S.
