Through efforts of the Global Polio Eradication Initiative (GPEI), begun in 1988, indigenous transmission of wild poliovirus (WPV) had been interrupted in all but four countries (Afghanistan, Pakistan, India, and Nigeria) by 2006.1 Since 2002, a total of 39 previously polio-free countries experienced outbreaks following importation of WPV of Indian or Nigerian origin.2- 4 Most outbreaks were stopped <6 months after confirmation. However, circulation in Angola, Chad, Democratic Republic of the Congo (DRC), and Sudan persisted >12 months following importation before 2009.3- 4 A key milestone of the GPEI 2010-2012 strategic plan5 was to interrupt WPV transmission in these African countries with reestablished transmission by the end of 2010. As of March 8, 2011, the milestone appeared to be on track only in Sudan. In Sudan, WPV type 1 (WPV1) was introduced in 2004, but no cases were detected for a 31-month period during 2005-2008. When resurgence occurred in 2008, surveillance and eradication efforts were enhanced, and no case has been detected since June 2009. In Chad, WPV type 3 (WPV3) transmission has persisted since 2007, although undetected for 7 months in 2010. In Angola, WPV1 circulation has persisted following importation in 2007, and became more widespread in 2010, with subsequent importations into DRC and Republic of the Congo (ROC). In DRC, WPV1 circulation has persisted since introduction in 2006. Achieving polio eradication depends on stopping WPV transmission in the four endemic countries and overcoming substantial, ongoing programmatic weaknesses in Chad, Angola, and DRC.