Four African countries have reported new cases of polio linked to the oral vaccine, as global health numbers show there are now more children being paralyzed by viruses originating in vaccines than in the wild. In a report late last week, the World Health Organization and partners noted nine new polio cases caused by the vaccine in Nigeria, Congo, Central African Republic and Angola. Seven countries elsewhere in Africa have similar outbreaks and cases have been reported in Asia. Of the two countries where polio remains endemic, Afghanistan and Pakistan, vaccine-linked cases have been identified in Pakistan. In rare cases, the live virus in oral polio vaccine can mutate into a form capable of sparking new outbreaks. All the current vaccine-derived polio cases have been sparked by a Type 2 virus contained in the vaccine. Type 2 wild virus was eliminated years ago. WHO and partners have long relied on oral polio vaccines because they are cheap and can be easily administered. Western countries use a more expensive injectable polio vaccine that contains an inactivated virus incapable of causing polio. The Independent Monitoring Board, a group set up by WHO to assess polio eradication, warned in a report this month that vaccine-derived polio virus is "spreading uncontrolled in West Africa." The group said officials were already "failing badly" to meet a recently approved polio goal of stopping all vaccine-derived outbreaks within 120 days of detection.