After it was announced earlier this month that two new cases of the poliovirus cropped up in Nigeria, details are starting to emerge of what exactly happened. According to health officials, the African nation has been polio-free for two years prior to the outbreak, however, the cases were both found in the northern part of the Borno State where raids by Boko Haram, an Islamic extremist group, have been abundant, therefore making it difficult for healthcare workers to access children in need of the lifesaving vaccine. Workers were able to trace the outbreak back to 2011, and believe it was likely dormant in the local sewage system.

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