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.

The FDA will require GSK and Pfizer to include on the label of their respiratory syncytial virus (RSV) vaccines a warning about the risk of developing Guillain-Barré syndrome (GBS), a rare neurological condition that can cause paralysis.

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

Barré for every million doses given.