RSV vaccines may slightly increase the risk of a rare neurological disorder
Vaccines against respiratory syncytial virus may have caused some cases of Guillain-Barré syndrome, a rare neurological disorder, federal health officials said Thursday.
The numbers were small, on the order of two cases per 100,000 people vaccinated or fewer, and much more data is needed to determine the risk, officials said. In May 2023, the Food and Drug Administration approved two vaccines against RSV: Abrysvo, from Pfizer, and Arexvy, from GSK.
In June, instead of recommending the vaccinations to all older adults, the Centers for Disease Control and Prevention recommended that adults age 60 or older, in consultation with their health care providers, could choose to receive a single dose of an RSV to get a vaccine. As of February 16, fewer than 10 million doses had been administered.
The new safety data, announced at a meeting of the agency’s scientific advisers, came from multiple databases maintained by federal health agencies. Still, due to the preliminary nature of the analysis, officials urged caution in interpreting the results.
“At this time, due to the uncertainties and limitations, these early data cannot determine whether there is an increased risk of GBS after vaccination in this age group,” said Dr. Thomas Shimabukuro, director of the CDC’s Immunization Safety Office, during a meeting. on Thursday.
Continued surveillance “will be better able to determine whether there is an increased risk of GBS after RSV vaccination, and if so, how great the risk is,” he said.
In Guillain-Barré syndrome, the immune system attacks the nerves. Most patients recover, but in severe cases the syndrome can lead to paralysis and death.
Experts noted that even if confirmed, the absolute risk remains low. The highest estimate from all databases puts the risk at approximately one case of GBS per 40,000 doses administered.
That rate is “very rare and should be seen in the context of the benefits of vaccination,” says Dr. Daniel Salmon, director of the Institute for Vaccine Safety at the Johns Hopkins Bloomberg School of Public Health.
RSV vaccines can prevent an estimated 120 to 140 hospital deaths and about 25,000 hospitalizations per million doses administered, federal officials said.
Most other side effects observed after vaccinations with the RSV vaccines were minor. But on January 19, federal health officials noted signs of an increase in Guillain-Barré syndrome after vaccination with Abrysvo.
Of the 37 preliminary reports in the Vaccine Adverse Event Reporting System, officials have verified 23 through medical record review, 15 at Abrysvo and eight after Arexvy, Dr. said. Shimabukuro. There were almost three additional cases of GBS per million doses of Abrysvo than would be expected in the population of older Americans.
A separate database identified four cases of GBS linked to Arexvy, for an estimated 14 cases per million doses administered. That system did not pick up any cases after admissions from Abrysvo. But the vaccine only accounted for about 10 percent of the total doses recorded in the database.
“I will say that these numbers are higher than the numbers we observed for high-dose flu and for Shingrix,” said Dr. Shimabukuro. (Shingrix is a vaccine against shingles.)
Additional data from the Centers for Medicare & Medicaid Services showed that the incidence of Guillain-Barré syndrome after vaccination with Abrysvo was approximately five times higher than expected. The incidence after vaccination with Arexvy was not statistically significant.
“These data are preliminary and there are several limitations to consider,” said Dr. Patricia Lloyd, a health statistician at the FDA.
GSK plans to study a possible link, said Alison Hunt, a company spokeswoman. “There are limitations to all of this data, and further analysis by the FDA, CDC and the vaccine manufacturers is needed to confirm and quantify any potential risk,” she said.
Pfizer did not immediately respond to a request for comment. A representative at Thursday’s meeting said the company was conducting four safety studies to monitor GBS
Rare cases of Guillain-Barré syndrome have been linked to other vaccines, including those against flu and shingles. Some cases were seen in the clinical trials of the two RSV vaccines, but the numbers were too small to be certain of a link.
RSV is especially dangerous for people with other chronic conditions.
During the 2017-2018 respiratory season, hospitalizations related to RSV were about 6.5 times higher for adults with chronic kidney disease, according to data presented Thursday. Those with other respiratory conditions, severe obesity or heart disease were also at increased risk.
By the end of December, about one in four Americans 60 and older with a chronic condition had received a dose of RSV vaccine, federal health officials said.