ON TOP of all the human misery inflicted upon the people of Syria by civil war, now comes the polio virus. The disease, which can lead to irreversible paralysis and death and strikes mostly children 5 and younger, can be spread in situations with poor hygiene and sanitation. The World Health Organization has confirmed 10 cases of wild polio virus in samples taken from Deir al-Zour province in northeastern Syria.

This is the scourge of war. Most of the polio cases are children 2 or younger, born and infected in the years in which Syria has been ravaged by violent conflict. The estimated polio immunization rate in Syria was 91 percent in 2010, but it fell to only 68 percent in 2012. The outbreak is a sign of what happens when health-care systems collapse. Most ominous, about half a million Syrian children have not been immunized. Vaccination is the most critical tool in the battle against polio, and a large-scale effort is being mounted to reach the unvaccinated children. Still, the World Health Organization has warned that the risk of further spread in the region is high, given the war, tides of refugees fleeing battle zones and big gaps in immunity. Efforts are being intensified to immunize children in Lebanon, Jordan, Iraq, Turkey, Israel and Egypt.

Elsewhere, impressive progress has been made in fighting polio. At the start of this year, the disease was endemic in only Pakistan, Nigeria and Afghanistan. Cases in these three countries are down 40 percent compared to last year, and southern Afghanistan has been free of it for a year. A major concern is North Waziristan, where vaccinators have been unable to reach children for more than a year, and where cases are on the rise. A severe outbreak in Somalia and one in Kenya have been tied to Nigeria. But polio has been stopped before in regions of conflict, and there is still hope that the disease can eventually be eradicated. Earlier this year, the Global Polio Eradication Initiative, an umbrella group, unveiled a promising strategy to reach zero cases in five years. Last year, the world saw only 223 polio cases, the lowest level in history. This year, the total is 322 and rising.

Until genetic analysis is complete, it won’t be possible to pinpoint the origin of the Syrian polio virus, but there are fears it spread from Pakistan. The challenge for Syria now is to carry out vaccinations amid the shooting. It is absolutely essential for frontline health workers to have access to the endangered populations. The Syrian Arab Red Crescent must be able to work without hindrance. The United Nations and Syria’s neighbors ought to demand that all sides — government forces and the opposition — guarantee that volunteers immunizing children do not become targets or victims. Roadblocks can stop fighters, but they will not stop polio virus, which threatens all in its path, the children of rebel fighters and army generals alike.