As many as 50 children have died as of Wednesday after receiving potentially spoiled or sabotaged measles vaccines in an area in northwestern Syria. Volunteer medical organizations in the area have suspended a campaign to prevent the spread of measles, rubella and polio.

The young victims, many infants, all died Tuesday in the cities of Jarjanaz and Sinjar in Idlib Province, which is controlled by forces against President Bashar al-Assad.

The civil war which began over three years ago has seen the collapse of the public health care system in Syria, and interim controllers have tried to provide basic care like vaccinations for children to Syrians.

Dozens more children reported to be sick from the vaccine in Idlib. Dr. Abdulla Ajaj, who helped provide the vaccine, said the doses had arrived three days before they were administered.

"This is the first time we have had such a problem," Ajaj said via a Skype interview with the New York Times. He believes the doses may have been improperly stored before they were given to his clinic. "Most probably they were badly kept inside the fridges."

However, other batches of the vaccine have been distributed via other physicians with none of the side effects seen in this area. Therefore, others suspect contaminants might have been in the vaccine vials or the diluting fluid.

Mohammad Hamadi, another Syrian doctor in the area, said that medical workers who dilute the vaccine, which comes in multiple-dose vials, may have accidentally mixed it with Atracurium, a muscle relaxant used in surgery. Hamadi said bottles of Atracurium look very similar to vaccine diluent containers.

"We are investigating if it's a mistake by the medical crew or a criminal act," he said.

Recipients of the bad measles vaccine displayed symptoms within minutes according to the Syrian American Medical Society, which runs a hospital in Idlib. This included slowed heart rate, wheezing and shortness of breath.