The FDA and CDC warned Thursday of a small increased risk of developing Guillain-Barré syndrome in older adults after immunization with respiratory syncytial virus vaccines from GSK and Pfizer.
Pictured: Elderly man getting vaccinated by a healthcare worker/iStock, dusanpetkovic
Respiratory syncytial virus vaccines could be increasing the risk of the rare autoimmune disorder Guillain-Barré syndrome in older adults, FDA and CDC officials warned Thursday, though the agencies said not enough data are available yet to draw definitive links.
In a presentation during Thursday’s Advisory Committee on Immunization Practices (ACIP) meeting, Tom Shimabukuro of the CDC’s Immunization Safety Office reported that as of February 16, 2024, the agency had detected 23 verified cases of Guillain-Barré syndrome (GBS), all occurring within 22 days of respiratory syncytial virus (RSV) vaccination.
Fifteen cases occurred in older adults who were given Pfizer’s Abrysvo, while the remaining eight patients had been immunized with GSK’s Arexvy. One patient died, though its unclear whether the mortality was linked with the shot or GBS, according to the CDC presentation.
In the 21 days following immunization, GBS was estimated to develop in 4.6 patients per 1 million doses of the Pfizer vaccine. The corresponding rate for GSK’s shot was 1.1 per 1 million doses. Since their respective launches, the Pfizer and GSK RSV vaccines have been administered to over 3 million and 6.5 million older adults, respectively, per CDC data.
GBS is a rare autoimmune disorder in which the immune system attacks the nerves. According to the CDC’s website, GBS manifests as muscle weakness and, uncommonly, paralysis. Its causes are not yet completely elucidated, though it often arises following an infection. In very rare cases, GBS develops following vaccination.
Of the 23 patients who developed GBS after receiving the RSV vaccines, 14 had also been immunized with other shots.
Pfizer and GSK are currently the industry’s leaders in the RSV vaccine space. GSK’s Arexvy was approved in May 2023 for use in older adults aged 60 years and above, beating out its competitor Abrysvo by a month. With this first-to-market advantage, GSK has claimed a huge slice of the market in the U.S., reaching 3 million of the potential 80 million patients as of December 2023.
The British pharma is working to expand Arexvy’s label to cover younger seniors. In October 2023, GSK posted early Phase III data demonstrating that the RSV shot was just as effective when used in adults aged 50 to 59 years.
GSK’s main competitor Pfizer has lagged far behind, with CFO David Denton saying in November 2023 that the company has been disappointed by Abrysvo’s launch. “If you look at our market share, I don’t think we performed as well as we thought we could,” Reuters reported at the time.
Besides older adults, Abrysvo is also approved for use in pregnant mothers from 32 weeks through 36 weeks of gestation to generate immunity in their infants. Pfizer is continuing to develop Abrysvo in children from two through 17 years and in adults aged 18 to 60 years.
Tristan Manalac is an independent science writer based in Metro Manila, Philippines. Reach out to him on LinkedIn or email him at tristan@tristanmanalac.com or tristan.manalac@biospace.com.
