American health authorities have warned that vaccines for respiratory syncytial virus (RSV) might have caused a few cases of the rare neurological condition Guillain-Barré syndrome, but said more data were needed to pin down the risk.
Thus far the numbers were small – two cases per 100 000 vaccinated people or fewer – reports The New York Times.
Last May, the US Food and Drug Administration approved two vaccines against RSV: Abrysvo, by Pfizer, and Arexvy, by GSK. In June, rather than recommend the shots to all older adults, the Centres for Disease Control and Prevention recommended that adults 60 or older might opt to receive a single dose of the vaccine in consultation with their doctors. Fewer than 10m doses had been administered by 16 February this year.
The new safety data, disclosed at a meeting of scientific advisers to the agency, came from multiple databases maintained by federal health agencies. But because of the preliminary nature of the analysis, officials urged caution in interpreting the results.
“At this point… these early data cannot establish if there is an increased risk for GBS after vaccination in this age group,” said Dr Thomas Shimabukuro, director of the CDC’s Immunisation Safety Office, last week
“Ongoing surveillance will be better able to determine if an increased risk is present, and its magnitude.”
Experts noted that even if confirmed, the absolute risk remains low. The highest estimate from any of the databases pegs the risk at about one case of GBS per 40 000 doses administered.
RSV vaccines may prevent an estimated 120 to 140 in-hospital deaths and about 25 000 outpatient visits per million doses administered, federal officials said.
Minor effects
Most of the other side effects observed after inoculations with the vaccines were minor, but in January, federal health officials picked up 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 by medical record review, 15 with Abrysvo and eight after Arexvy. There were nearly 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, translating to an estimated 14 cases per million doses administered. That system did not pick up any cases after shots of Abrysvo. But the vaccine accounted for only about 10% of the total doses recorded in the database.
Additional data from the Centres for Medicare & Medicaid Services showed the incidence of Guillain-Barré syndrome after vaccination with Abrysvo was roughly five times higher than would be expected. The incidence after vaccination with Arexvy was not statistically significant.
GSK is planning to study a possible link, said a spokeswoman for the company. “There are limitations to all of these data, and further analysis by FDA, CDC, and the vaccine manufacturers, are needed to confirm and quantify any potential risk.”
A Pfizer representative at the meeting said the company was conducting four safety studies that monitor GBS.
Rare cases of Guillain-Barré syndrome have been linked to other vaccines, including those against influenza and shingles. A few cases were observed in the clinical trials of the two RSV vaccines, but the numbers were too small to be certain of an association.
RSV is particularly dangerous for those with other chronic conditions.
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