Health officials have added an updated warning about rare side effects linked to RSV vaccines offered to older adults and pregnant women. The concern involves Guillain-Barré syndrome, a neurological condition that affects the nerves and can cause weakness, numbness, and movement problems.

The warning followed a U.S. Food and Drug Administration review of two RSV vaccines, including Abrysvo, which is also used in the UK. Researchers found a small increase in cases of Guillain-Barré syndrome within 42 days after vaccination.

For Abrysvo, the study found about nine additional cases per one million doses. Another RSV vaccine, Arexvy, showed around seven extra cases per one million doses. Officials noted this is still rare, and the benefits of vaccination continue to outweigh the risks for vulnerable groups.

RSV, or respiratory syncytial virus, often causes cold-like symptoms, but it can be dangerous for older adults, newborn babies, and people with weaker immune systems. It can lead to serious breathing problems, pneumonia, and hospital admissions, especially during winter months.

Doctors say Guillain-Barré syndrome is usually temporary with treatment, although some people may take longer to recover. Health experts continue to recommend the RSV vaccine, especially for adults aged 75 to 79 and pregnant women after 28 weeks, while making sure patients are aware of the rare possible risks.