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 fewer, 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 vaccines for all older adults, the Centers for Disease Control and Prevention recommended that adults age 60 and older could choose to receive a single dose of the RSV vaccine in consultation with your health care providers. As of February 16, fewer than 10 million doses had been administered.
The new safety data, released at a meeting of the agency’s scientific advisers, comes from multiple databases maintained by federal health agencies. Still, due to the preliminary nature of the analysis, officials urged caution when interpreting the results.
“At this time, due to uncertainties and limitations, these early data cannot establish whether there is an increased risk of GBS after vaccination in this age group,” Dr. Thomas Shimabukuro, director of the Bureau, said at a meeting. CDC Immunization Safety Policy. Thursday.
Continued surveillance “will be able to better determine whether there is an increased risk of GBS following 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 cause paralysis and death.
Experts noted that even if confirmed, the absolute risk remains low. The highest estimate from either database pegs the risk at approximately 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 can prevent about 120 to 140 hospital deaths and about 25,000 hospitalizations per million doses administered, federal officials said.
Most other side effects observed after inoculations with RSV vaccines were minor. But on January 19, federal health officials detected signs of an increase in Guillain-Barré syndrome after inoculation with Abrysvo.
Of 37 preliminary reports in the Vaccine Adverse Event Reporting System, officials verified 23 through medical record review, 15 with Abrysvo and eight after Arexvy, Dr. Shimabukuro said. There were almost three additional cases of GBS per million doses of Abrysvo than would be expected in the older American population.
A separate database identified four cases of GBS linked to Arexvy, which translates to approximately 14 cases per million doses administered. That system did not detect any cases after the Abrysvo shootings. But the vaccine represented only about 10 percent of the total doses recorded in the database.
“I will say that these rates are higher than the rates we have seen for high-dose influenza and for Shingrix,” Dr. Shimabukuro said. (Shingrix is a shingles vaccine.)
Additional data from the Centers for Medicare and Medicaid Services indicated 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 note,” said Dr. Patricia Lloyd, an FDA health statistician.
GSK plans to study a possible link, said company spokeswoman Alison Hunt. “All of this data has limitations and further analysis is needed by the FDA, CDC, and vaccine manufacturers to confirm and quantify any potential risks,” 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 monitoring GBS.
Rare cases of Guillain-Barré syndrome have been linked to other vaccines, including influenza and shingles. Some cases were seen in clinical trials of the two RSV vaccines, but the numbers were too small to be sure of an association.
RSV is particularly dangerous for those 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. People with other respiratory conditions, severe obesity or heart disease were also at higher risk.
As of late December, about one in four Americans age 60 and older with a chronic illness had received a dose of the RSV vaccine, federal health officials said.
