Ongoing violence in Syria has hindered an international campaign to administer polio vaccines to thousands of children, just months after experts confirmed the countrys first polio cases in more than a decade. United Nations aid groups announced yesterday that fighting in the northeast province of Raqqa has brought the vaccination campaign to a halt, putting 100,000 children at risk of infection. As Reuters reports, the groups are appealing for access to the region, which is the only province under the control of armed rebel groups. We havent reached Raqqa town in this second round of immunization, Elizabeth Hoff of the World Health Organization (WHO) told Reuters.