 A small number of additional cases in Nigeria, caused by WPV1, were viewed as a setback, the first being detected there in almost two years, yet the virus had been circulating undetected in regions inaccessible due to the activities of Boko Haram.There was also a cVDPV1 outbreak in Laos, while new strains of cVDPV2 arose separately in Nigeria's Borno and Sekoto states, and in the Quetta area of Pakistan, collectively causing five cases.Because cVDPV2 strains continued to arise from trivalent oral vaccine that included attenuated PV2, this vaccine was replaced with a bivalent version lacking WPV2 as well as trivalent injected inactivated vaccine that cannot lead to cVDPV cases.