GSK and Pfizer's respiratory syncytial virus (RSV) vaccines will carry warnings that they can increase the risk of developing a rare neurological disorder, the U.S. Food Drug Administration said on Tuesday.

On Tuesday, January 7, the FDA announced it would now be requiring GSK and Pfizer’s RSV vaccines to hold warnings of a risk of Guillain-Barré syndrome (GBS). This is after post market analysis by the American regulator.

As for GBS itself, this neurological ailment can be severe, attacking nerves and warranting hospitalisation for weeks or months. It can influence a variety of nerves from senses to movement, and even heart rhythm, with initial symptoms manifesting typically in the limbs.

Barré syndrome, although it said data don’t prove a causal link and affirmed the shots’ benefit outweighs their risks.

FDA updates safety labels for Pfizer's Abrysvo and GSK's Arexvy RSV vaccines, citing increased Guillain-Barré syndrome risk. Study estimates 7-9 excess GBS cases per million doses.

Barré for every million doses given.