Reported iVDPV cases from 1960 to November 2012. This figure demonstrates the geographical representation of the iVPDV cases identified in our review, and the corresponding number of cases for each respective country. Twenty-five countries and the Palestinian territories (West Bank and Gaza Strip) reported iVDPV cases, although most countries reported only one case. Half (n = 34) of cases included in our analysis were from four countries: Iran, the United States, U.K., and China. Nine cases were reported in four African countries. More countries in Asia and the Middle East appear to have reported ≥1 case, but iVDPV case incidence was not isolated to a particular region.