Philippine health officials investigating the anti-dengue vaccine Dengvaxia announced Friday that the drug may be linked to the deaths of three children.

The Philippine General Hospital Dengue Investigative Task Force (DITF) worked with an independent group of experts that reviewed 14 deaths among vaccine recipients. The task force determined that three cases had causal association with Sanofi’s vaccine.

“The children died due to dengue despite being vaccinated with Dengvaxia — two of which may be on account of vaccine failure,” the DITF stated, warranting further testing of tissue samples and antibodies to finish the investigation.

The investigation results were a factor in the task force’s decision to suspend the Dengue Immunization Program, which stated that Dengvaxia is “not fit for a mass immunization program that does not screen for prior dengue infection and comorbidities of children before the administration of the vaccine.”

The vaccine has been under fire for posing risks to patients who have no prior infection, with some 700,000 youths being vaccinated with the drug under the country’s mass immunization program.