A couple of paragraphs up in the Wikipedia article: "Oral polio vaccine results in vaccine-associated paralytic poliomylelitis in about three per million doses". I've also seen one in two million doses quoted elsewhere, but it's somewhere around the one in a million mark. You coupld probably quibble about whether that really counts as getting polio, but it's paralysis caused by infection with poliovirus and there is "no clinical difference between the paralysis caused by wild poliovirus, OPV, or VDPV" according to the CDC's FAQ on the topic so that's not a particularly interesting semantic quibble to me.