A post-marketing review by the FDA detected an increased risk of the autoimmune condition in patients inoculated with GSK’s Arexvy and Pfizer’s Abrysvo, prompting the regulator to require adjustments to the vaccines’ labels.
The FDA on Tuesday required GSK and Pfizer to include warnings about Guillain-Barré syndrome risk in the labels for their respiratory syncytial virus vaccines.
The directive follows a post-marketing study by the regulator, which found that patients inoculated with GSK’s Arexvy and Pfizer’s Abrysvo are at greater risks of developing GBS, a rare neurological disorder characterized by weakness, tingling in the extremities and, in severe cases, paralysis.
“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 FDA wrote. Results of the post-marketing study, which relied on Medicare claims data, showed nine excess cases of GBS per million Abrysvo doses and seven excess cases per million Arexvy inoculations in adults 65 years and above.
The GBS safety risk will not be reflected in boxed warnings—considered as the FDA’s most serious precautionary signal—but instead will appear in the Warnings and Precautions section of the vaccines’ respective labels. It applies to the 42 days following vaccination.
Tuesday’s safety update is the latest blow to RSV vaccine developers. In June 2024, the U.S. Centers for Disease Control and Prevention (CDC) updated its inoculation guidelines, narrowing the recommended use of RSV shots to all seniors 75 years and above and those 60 to 74 years who are at risk of severe disease. Previously, RSV vaccines were recommended in all adults 60 and older.
A few months later, the CDC reaffirmed these new guidelines, insisting that the benefits of RSV vaccination outweighed its risks in these specific elderly populations. Meanwhile, for adults below 60 years, the CDC’s Advisory Committee on Immunization Practices argued that data so far have not “motivated an immediate policy expansion,” with existing evidence pointing to “increasing certainty” that the shots are linked to GBS risk.
These adjusted ages are expected to hurt RSV vaccine sales. In an October 2024 report, analytics firm Airfinity lowered its annual revenue estimates for the shots to $1.7 billion by 2030. This figure represents a 64% drop from its prior projection of $4.6 billion.
In addition, the FDA’s Vaccines and Related Biological Products Advisory Committee last month found that two of Moderna’s experimental RSV vaccine are potentially linked to an imbalance in severe lower respiratory tract infection in infants. Still, the panelists insisted that there is not enough information to conclusively recommend discontinuing the candidates’ development, and urged the FDA and the pharma to continue testing.
The RSV vaccine space is dominated by GSK and Pfizer, with the former being the undisputed leader. Arexvy was approved in May 2023—one month ahead of Pfizer’s Abrysvo—and raked in nearly $1.6 billion by the end of 2023. Abrysvo’s 2023 earnings, in comparison, sat at $515 million.
