12:49 PM EST, 01/08/2025 (MT Newswires) -- (Updates with GSK's comments in seventh, eighth and ninth paragraphs.)

GSK (GSK) and Pfizer's ( PFE ) respiratory syncytial virus vaccines will carry warnings of increased risk of Guillain-Barre Syndrome, the US Food and Drug Administration said Tuesday on its website.

Results from a post-marketing observational study suggested an increased risk of Guillain-Barre Syndrome (GBS) during the 42 days after vaccination with Pfizer's ( PFE ) Abrysvo and GSK's Arexvy, the FDA said.

GBS is a rare disorder in which the body's immune system damages nerve cells, causing muscle weakness and sometimes paralysis.

The FDA said it has "determined that the overall body of evidence suggests increased risks of GBS with Abrysvo and Arexvy, but that available evidence is insufficient to establish a causal relationship."

"FDA has required and approved safety labeling changes to the Prescribing Information for Abrysvo and Arexvy," the regulator said.

"FDA has further determined that the benefits of vaccination with Abrysvo and Arexvy continue to outweigh their risks," it added.

A GSK spokesperson told MT Newswires that "GBS risk following RSV vaccination is rare, with fewer than 10 cases per one million vaccinations."

"While the results of this observational study suggest an increased risk of GBS with Arexvy, available evidence is insufficient to establish a causal relationship," the GSK spokesperson said, adding that the vaccine has been given "to over 9 million people in the US and has an overall acceptable safety profile."

"GSK has ongoing studies to further evaluate safety, including any potential association with GBS," the spokesperson said.

Pfizer ( PFE ) didn't immediately respond to a request for comment by MT Newswires.

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