Sixteen of the paralyzed children were from Mayadin, south of Deir al-Zour, and one was from farther north in Raqqa, the Syrian redoubt of the Islamic State extremist group. The entire region has been upended by fighting.
All of the children developed the paralysis between March 3 and May 23, Mr. Jasarevic said.
Unlike Syria’s first polio outbreak in 2013, caused by a wild strain that paralyzed 36 children before it was brought under control, the new outbreak derived from the polio vaccine itself, Mr. Jasarevic said.
The vaccine, a weakened form of the polio virus that triggers the immune system’s response, is secreted in the waste of vaccinated children, and over time can mutate into an infectious strain that may afflict the unvaccinated. The risks are especially high in areas where not all children have received the vaccine and where the mutated virus can spread from contaminated sewage or water.
“These vaccine-derived outbreaks really are a marker of poor vaccination and poor sanitation in the community,” said Dr. Homer Venters, director of programs at Physicians for Human Rights, an international aid group based in New York that supports humanitarian work in war zones, including Syria and Yemen.
Along with a recent measles outbreak near Damascus, the Syrian capital, and a cholera scourge raging in war-torn Yemen, Dr. Venters said, the new polio outbreak “is another indication that public health systems have been decimated by these conflicts.”
As of late March and April, Mr. Jasarevic said, there had been some vaccinations in parts of the Deir al-Zour area, “but security remained an issue and that’s why many children were not vaccinated.”
He also said it was unclear whether the afflicted child in Raqqa meant that the virus was circulating there or whether the child had traveled to Raqqa and then developed the case.