The World Health Organization says it has discovered two additional cases of the highly contagious polio virus in Syria, bringing the total number of cases in the country to 17.

Sona Bari, an official with the U.N. agency said the new cases are in Aleppo and in rural Damascus—far from where the first was discovered in the northeast province of Deir el-Zour in early November.

Those cases were the first discovered in Syria for over a decade, caused by the collapse of the health system in conflict areas. Half a million children were left without vaccinations.

Following the outbreak, the U.N. began its largest polio vaccination campaign in the region's history, trying to vaccinate and re-vaccinate 20 million children from Iraq to Turkey.