Two adults over 60 developed Guillain-Barre syndrome after receiving Pfizer's respiratory syncytial virus vaccine candidate in a phase 3 trial. Now the FDA is asking the pharmaceutical giant to conduct a safety study.
"Given the temporal association and biological plausibility, FDA agrees with the assessments of the investigators that these events were possibly related to study vaccine," an FDA spokesperson told CNBC.
The control group in the trial that did not receive a vaccine did not have any cases of Guillain-Barre syndrome. However, in a briefing document, Pfizer notes that in one of the two cases, "after discussion with the participant's neurologist, the investigator considered that there is a possibility that the patient's [Guillain-Barre syndrome] was related to blinded study intervention."
In both cases, the patients' Guillain-Barre syndrome symptoms resolved after three to six months, CNBC reports.