■Officials are investigating more than 20 cases of Guillain-Barre syndrome.

■Two-thirds of the cases occurred in people who got Pfizer’s vaccine.

■CDC officials also presented estimates that the benefits of vaccination outweigh possible risks.

NEW YORK — Health officials are investigating whether there’s a link between two new RSV vaccines and cases of a rare nervous system disorder in older U.S. adults.

The inquiry is based on fewer than two dozen cases seen among more than 9.5 million vaccine recipients, health officials said Thursday. And the available information is too limited to establish whether the shots caused the illnesses, they added.

But the numbers are higher than expected and officials are gathering more information to determine if the vaccines are causing the problem. The data was presented at a meeting of an expert panel that provides vaccine policy advice to the Centers for Disease Control and Prevention.

Guillain-Barre Syndrome

Officials said they were investigating more than 20 cases of Guillain-Barre syndrome, an rare illness in which a person’s immune system damages nerve cells, causing muscle weakness and paralysis. An estimated 3,000 to 6,000 people develop GBS in the U.S. each year, and it’s more commonly seen in older people, according to the CDC.

Most people fully recover from the syndrome, but some have permanent nerve damage. Guillain-Barre can occur in people after they are infected with a virus, but in some instances cases have been linked to vaccinations.

About RSV

RSV, or respiratory syncytial virus, is a common cause of cold-like symptoms but it can be dangerous for infants and the elderly.

Last year, the CDC signed off on a recommendation made by the advisory panel, aimed at Americans age 60 and older. It was for a single dose of RSV vaccine. There were two options, one made by Pfizer and the other by GSK.

Officials were aware that instances of Guillain-Barre had been identified in clinical trials done before the shots were approved for sale, and that different systems were watching for signs of problems.

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Analysis of Reports

At a meeting of the expert panel on Thursday, CDC officials presented an analysis of the reports taken in by those systems.

About two-thirds of the cases occurred in people who got a version of the vaccine made by Pfizer, called Abrysvo. But officials are also doing follow-up tracking in people who got Arexvy, made by GSK.

About two cases of Guillain-Barre might be seen in every 1 million people who receive a vaccine, health officials estimate. A CDC analysis found the the GSK rate was lower than that, but 4.6 cases per million were reported in recipients of the Pfizer shot.

Data from the U.S. Food and Drug Administration also showed an above-expected number of Guillain-Barre cases being reported in RSV vaccine recipients, with more among Pfizer shot recipients.

Increased Risk

“Taken together, these data suggest a potential increased risk” in RSV vaccine recipients 60 and older that must be explored, said Dr. Tom Shimabukuro, a CDC vaccine safety monitoring official.

Officials from GSK and Pfizer made brief statements during the meeting, noting that sorting out a safety signal is complicated.

“Pfizer is committed to the continuous monitoring and evaluation of the safety of Abrysvo” and is conducting four safety studies to look into the possibility of vaccine-related GBS, said Reema Mehta, a Pfizer vice president.

Vaccine Benefits

CDC officials also presented estimates that the vaccines have prevented thousands of hospitalizations and hundreds of deaths from RSV, and that current data indicates the benefits of vaccination outweigh the possible risks.