The FDA has mandated that Pfizer and GSK update the safety labels for their respective respiratory syncytial virus (RSV) vaccines, Abrysvo and Arexvy, to include a warning regarding the potential increased risk of Guillain-Barré syndrome (GBS). This decision follows postmarketing observational studies that suggested a higher incidence of GBS within 42 days after vaccination with either vaccine, particularly in adults aged 65 and older. While the FDA has not established a causal link between the vaccines and GBS, the agency has determined that the available evidence warrants the inclusion of this warning in the prescribing information.
Postmarketing Data and GBS Risk
The FDA's decision is based on a comprehensive review of data from clinical trials, reports to the Vaccine Adverse Event Reporting System (VAERS), and a postmarketing observational study. The postmarketing study, which analyzed Medicare claims data from May 2023 to July 2024, identified an increased risk of GBS within 42 days following vaccination with Abrysvo and Arexvy. Specifically, the analysis estimated nine excess cases of GBS per million doses of Abrysvo and seven excess cases per million doses of Arexvy administered to individuals 65 years of age and older.
It is important to note that the FDA has emphasized that the available evidence is insufficient to establish a causal relationship between the RSV vaccines and GBS. The agency stated 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."
Guillain-Barré Syndrome (GBS)
GBS is a rare neurological disorder in which the body's immune system mistakenly attacks part of its peripheral nervous system. This can lead to muscle weakness, loss of reflexes, and, in severe cases, paralysis. GBS can be life-threatening if it interferes with breathing, blood pressure, or heart rate. While most people eventually recover from GBS, some may experience long-term weakness or other residual effects.
Continued Monitoring and Benefit-Risk Assessment
Despite the GBS warning, the FDA has affirmed that the benefits of Abrysvo and Arexvy in preventing RSV-related lower respiratory tract disease (LRTD) continue to outweigh the risks. RSV is a common respiratory virus that can cause severe illness, particularly in older adults and infants. The FDA estimates that each million doses of RSV vaccine administered could prevent nearly 10,000 hospitalizations in adults aged 60 and older.
The FDA is committed to continuous monitoring and assessment of the safety of all vaccines. The agency encourages healthcare professionals and patients to report any adverse events following vaccination to VAERS.
Company Statements
Both Pfizer and GSK have issued statements acknowledging the FDA's decision and reaffirming their commitment to monitoring the safety of their RSV vaccines.
A GSK spokesperson stated, "While the results of this observational study suggest an increased risk of GBS with Arexvy, available evidence is insufficient to establish a causal relationship. Arexvy has been administered to over 9 million people in the U.S. and has an overall acceptable safety profile."
A Pfizer spokesperson noted that flu vaccines have also been associated with GBS and that the company will continue to monitor the safety of Abrysvo.
