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Number of cases of wild poliovirus types 1 (WPV1), 3 (WPV3), and 1 and 3 (WPV1/WPV3), and circulating vaccine-derived poliovirus type 2 (cVDPV2), by month—Pakistan, 2010–2013. Abbreviations: bOPV, bivalent oral polio vaccine, types 1 and 3; mOPV, monovalent oral polio vaccine, type 1 or 3; NID, national immunization day; SNID, subnational immunization day; tOPV, trivalent oral polio vaccine.
