R.S.V. Vaccines May Slightly Increase Risk of Rare Neurological Condition

Vaccines for respiratory syncytial virus may have caused a few cases of Guillain-Barré syndrome, a rare neurological condition, federal health officials said on Thursday.

The numbers were small, on the order of two cases per 100,000 vaccinated people or fewer, and much more data is needed to pin down the risk, the officials said. In May 2023, the Food and Drug Administration approved two vaccines against R.S.V.: Abrysvo, by Pfizer, and Arexvy, by GSK.

In June, rather than recommend the shots to all older adults, the Centers for Disease Control and Prevention recommended that adults aged 60 or older might opt to receive a single dose of an R.S.V. vaccine in consultation with their health care providers. Fewer than 10 million doses had been administered by Feb. 16.

The new safety data, disclosed at a meeting of scientific advisers to the agency, came from multiple databases maintained by federal health agencies. Still, because of the preliminary nature of the analysis, officials urged caution in interpreting the results.

“At this point, due to the uncertainties and limitations, these early data cannot establish if there is an increased risk for G.B.S. after vaccination in this age group,” Dr. Thomas Shimabukuro, director of the C.D.C.’s Immunization Safety Office, said at a meeting on Thursday.

Ongoing surveillance “will be better able to determine if an increased risk for G.B.S. after R.S.V. vaccination is present, and if so the magnitude of the risk,” he said.