The FDA will require GSK and Pfizer to include on the label of their respiratory syncytial virus (RSV) vaccines a warning about the risk of developing Guillain-Barré syndrome (GBS), a rare neurological condition that can cause paralysis.
The ruling will affect GSK’s Arexvy and Pfizer’s Abrysvo, both of which were approved by the agency in May of 2023 for adults 60 years or older and realized booming sales in their first year on the market.
Seven months ago, however, the sales potential for both shots declined significantly when the Centers for Disease Control and Prevention (CDC) recommended that they only be used by adults age 75 and older and those 60 and older who have a high risk of severe disease due to underlying medical conditions.
In narrowing the population with its revised recommendation, the CDC cited the potential link between the vaccines and GBS.
On Tuesday, the FDA explained that its new guidelines come after the agency conducted a postmarketing observational study and evaluated the results of clinical trials and reports to its Vaccine Adverse Event Reporting System (VAERS).
Using Medicare claims data, the FDA determined that there is an increased risk of developing GBS in a 42-day window after RSV vaccination. For adults age 65 and older, there are an estimated nine cases of GBS per million doses of Pfizer’s Abrysvo and an estimated seven cases of GBS per million doses of GSK’s Arexvy, the FDA said.
“FDA has determined that the overall body of evidence suggests increased risks of GBS with Abrysvo and Arexvy, but that available evidence is insufficient to establish a causal relationship,” the agency said in a safety communication.
While issuing its RSV warning mandate on Tuesday, the FDA added that the benefits of vaccination with Abrysvo and Arexvy “continue to outweigh their risks.” During an FDA advisory panel meeting in October, the agency pointed out that each million of RSV vaccine doses administered could prevent nearly 10,000 hospitalizations in adults aged 60 and older.
“While the results of this observational study suggest an increased risk of GBS with Arexvy, available evidence is insufficient to establish a causal relationship,” a GSK spokesperson said. “Arexvy has been administered to over 9 million people in the U.S. and has an overall acceptable safety profile.”
“With 64 million people impacted by RSV globally and nearly half a million adults hospitalized in high income-countries every year, RSV vaccines respond to a significant unmet medical need,” GSK's spokesperson added on Wednesday.
A Pfizer spokesperson reminded in an email that flu vaccines also have been associated with GBS.
“If there is an increased risk of GBS following flu vaccination, it is small, on the order of one to two additional GBS cases per million doses of flu vaccine administered,” according to the CDC.
Additionally, in 2021, GBS cases were tied to the use of Johnson & Johnson’s COVID-19 vaccine.
In 2023, GSK reported that Arexvy generated (PDF) sales of 1.238 million pounds sterling ($1.5 billion). In October, however, the company said that third-quarter sales of the shot had declined by 74% year over year to 188 million pounds sterling ($244 million).
In October, Pfizer reported a 5% year-over-year downturn in its third-quarter sales of Abrysvo. In 2023, the shot racked up (PDF) $890 million.
Earlier this week—in a letter to shareholders—Moderna CEO Stéphane Bancel acknowledged a “contraction” of the RSV market and the resulting decline in the prospects of the company’s mRESVIA shot, which was approved in May of last year and generated just $10 million in sales in the third quarter. Moderna’s vaccine has not been tied to GBS.
Six months ago, after the CDC panel narrowed its recommendations on who should receive RSV shots, London-based healthcare analytics company Airfinity sliced its 2030 RSV market value projection for seniors in the US from $4.7 billion to $1.7 billion.