FDA warns of Guillain-Barre syndrome as possible risk of Pfizer’s RSV vaccine

The Food and Drug Administration has flagged Guillain-Barre syndrome, a rare neurological condition, as a potential risk for Pfizer’s respiratory syncytial virus vaccine.

Two people in their 60s who received the shot were diagnosed with Guillain-Barre syndrome, out of about 20,000 vaccine recipients who participated in Pfizer’s Phase 3 clinical trial, according to the FDA document. One person’s illness had completely resolved after three months, while the other continues to show signs of improvement six months later.

There were no cases in the trial’s placebo group or among those who did not receive the shot.

Guillain-Barre syndrome, or inflammatory neuropathy, is a disorder in which the body’s immune system mistakenly attacks the nerves. Symptoms can range from bursts of weakness to paralysis, according to the National Institutes of Health. It causes anywhere from 6,000 to 10,000 deaths a year among seniors, though mortality rates tend to vary from season to season.

However, most people recover, even from the most severe cases.

“Given the temporal association and biological plausibility, FDA agrees with the assessments of the investigators that these events were possibly related to [the] study vaccine,” said the FDA. “Therefore, [Guillain-Barre] is being considered an important potential risk.”

Pfizer, in its briefing document, said the cases have other possible explanations, adding that its shot is a “well-tolerated and safe vaccine, with a benefit-to-risk ratio that is favorable.” The New York-based pharmaceutical company also agreed to conduct a safety study to further assess potential risks of Guillain-Barre syndrome should the vaccine be approved.

The FDA documents were released ahead of a meeting next week of its independent vaccine advisers, the Vaccines and Related Biological Products Advisory Committee. On Tuesday, they will vote on whether Pfizer’s efficacy and safety data warrants an FDA approval.

Pfizer’s vaccine was 85% effective at preventing the lower respiratory tract illness for which it was designed.

So far, no approved RSV vaccine exists.