The Nigerian government has reported two new polio cases in the first reemergence of the disease since 2014, the World Health Organization (WHO) said Thursday. 

Two children in the northeast state of Borno had been paralysed by the disease, the Geneva-based group said in a statement. The new cases represent a major setback for Nigeria, which had just celebrated two years without polio last month and was on track to be certified free of the virus in July 2017.