What Is Guillain-Barre Syndrome? Symptoms, Treatment As Disease A 'Risk' Of Pfizer RSV Vaccine

Two elderly people developed a rare immune system disorder after receiving an in-development Pfizer vaccine, prompting the Food and Drug Administration (FDA) to request the pharmaceutical giant to propose a safety study should the shot ever be released on the market.

The two, a male and female, aged 66, were part of clinical trials for RSVpreF, Pfizer's Respiratory Syncytial Virus Infection (RSV) vaccine candidate, according to the FDA's Vaccines and Related Biological Products Advisory Committee.

They were the only people among 19,942 vaccinated participants to develop Guillain-Barré syndrome (GBS) after receiving the vaccine, which has been trademarked as Abrysvo, the FDA said in a briefing document dated Feb. 28, 2023.

The Centers for Disease Control and Prevention (CDC) defined RSV as a "common respiratory virus that usually causes mild, cold-like symptoms," while GBS "a rare disorder where the body's immune system damages nerves."

"Doctors usually treat GBS disease with antibiotics. Sometimes people with soft tissue and bone infections may need additional treatment, such as surgery," the health agency explained.

The male participant, who had hypertension before developing GBS, was hospitalized for several days, but his symptoms resolved around six months after they appeared, according to the FDA.

In contrast, the female participant developed a rare form of GBS called Miller-Fisher syndrome, characterized by problems with eye movement and/or blurry vision as well as loss of coordination in the arms and legs, among other symptoms.

She was hospitalized for fatigue and unstable movements before her symptoms resolved around three months following their onset.

A total of 396 serious adverse events were observed during RSVpreF's clinical trials, but only the two GBS cases and a case of hypersensitivity were deemed by the FDA to have been related to the vaccine.

Pfizer, for its part, reportedly assessed that the three cases were unrelated to RSVpreF.

As the background rate for GBS in the United States among adults over the age of 60 is approximately 1.5 to 3 cases per 100,000 annually, the disease is now considered an "important potential risk," according to the briefing.

The FDA has advised Pfizer to identify GBS as such and to submit a proposal for a post-marketing safety study to assess the risk of the disease and other immune-mediated demyelinating conditions in people who will receive RSVpreF.

The agency has also recommended that Pfizer conduct enhanced pharmacovigilance activities for all cases of GBS and other immune-mediated demyelinating conditions, as well as submit a summary and analysis of all such cases in a report.