Respiratory syncytial virus vaccines may have caused some cases of Guillain-Barré syndrome, a rare neurological condition, federal health officials said Thursday.
The numbers were small, on the order of two cases per 100,000 vaccinated people or less, and much more data is needed to pinpoint the risk, officials said. In May 2023, the Food and Drug Administration approved two RSV vaccines: Pfizer’s Abrysvo and GSK’s Arexvy.
In June, instead of recommending the vaccines for all seniors, the Centers for Disease Control and Prevention recommended that adults age 60 and older choose to receive a single dose of RSV vaccine in consultation with their health care providers. Fewer than 10 million doses had been administered by February 16.
The new safety data, revealed at a meeting of the agency’s scientific advisors, came from multiple databases maintained by federal health agencies. However, due to the preliminary nature of the analysis, officials urged caution in interpreting the results.
“At this point, due to uncertainties and limitations, these early data cannot prove whether there is an increased risk of GBS after vaccination in this age group,” said Dr. Thomas Shimabukuro, director of CDC’s Office of Vaccine Safety. , At a meeting. on Thursday.
Continued surveillance “will be better able to determine whether there is an increased risk for GBS after RSV vaccination and, if so, the magnitude of the risk,” 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 any of the databases links the risk to about one case of GBS per 40,000 doses administered.
That rate is “very rare and should be considered in the context of the benefits of vaccination,” said Dr. Daniel Salmon, director of the Institute for Vaccine Safety at the Johns Hopkins Bloomberg School of Public Health.
RSV vaccines may prevent about 120 to 140 in-hospital deaths and about 25,000 hospitalizations per million doses given, federal officials said.
Most of the other side effects seen after vaccinations with the RSV vaccines were minor. But on Jan. 19, federal health officials found signs of an increase in Guillain-Barré syndrome after the Abrysvo vaccination.
Of the 37 preliminary reports to the Adverse Vaccine Event Reporting System, officials verified 23 with medical record review, 15 with Abrysvo and eight after Arexby, Dr. Shimabukuro said. There were almost three more cases of GBS per million doses of Abrysvo than would be expected in the elderly American population.
A separate database found four cases of GBS linked to Arexvy, which translates to about 14 cases per million doses administered. This system caught no chance after Abrysvo’s shot. But the vaccine accounted for only about 10% of the total doses recorded in the database.
“I will say that these rates are higher than the rates we’ve seen for high-dose flu and for Shingrix,” Dr. Shimabukuro said. (Shingrix is a shingles vaccine.)
Additional data from the Centers for Medicare & Medicaid Services showed that the incidence of Guillain-Barré syndrome after vaccination with Abrysvo was about five times higher than expected. The incidence after vaccination with Arexvy was not statistically significant.
“These data are preliminary and there are several limitations that must be considered,” said Dr. Patricia Lloyd, a health statistician at the FDA.
GSK plans to study a possible tie-up, said Alison Hunt, a company spokeswoman. “There are limitations to all of these data, and further analysis by the FDA, CDC and vaccine manufacturers is needed to confirm and quantify any potential risk,” he said.
Pfizer did not immediately respond to a request for comment. A spokesman at Thursday’s meeting said the company has conducted four safety studies tracking GBS
Rare cases of Guillain-Barré syndrome have been linked to other vaccines, including those against influenza and shingles. A few cases were seen in clinical trials of the two RSV vaccines, but the numbers were too small to be certain that there is an association.
RSV is especially dangerous for people with other chronic conditions.
During the 2017-18 respiratory season, RSV-related hospitalizations 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 age 60 and older with a chronic condition had received a dose of RSV vaccine, federal health officials said.
