After decades of research into respiratory syncytial virus (RSV), Pfizer and GSK’s groundbreaking vaccines made waves as the first immunizations against the common respiratory illness.
Now, health officials are probing a possible link between the shots and the rare neurological disorder Guillain-Barré syndrome (GBS).
At a meeting of the CDC's Advisory Committee on Immunization Practices (ACIP), health officials presented a preliminary statistical analysis that discovered 23 of the some 9.5 million older adults who received an RSV vaccine developed GBS, an illness in which the immune system attacks the nerves.
In the 21-day period after vaccination, the rate of GBS among recipients of Pfizer’s Abrysvo was 4.6 per 1 million vaccine doses, according to the preliminary data. In people who received GSK’s Arexvy, the GBS rate came out to 1.1 per 1 million.
In total, 15 GBS cases were identified after an Abrysvo injection and eight after Arexvy, the director of the CDC’s immunization safety office, Thomas Shimabukuro, said at the meeting.
The analysis is by no means conclusive and comes with a number of limitations. For one, GBS is a “rare outcome,” which raises uncertainty and poses a “challenge for verification of a potential signal,” the officials said in their presentation.
The vaccine makers were present at the meeting and stressed their commitment to further research on the potential risk.
Pfizer's head of risk assessment and safety, Reema Mehta, told the committee that certain considerations, such as underlying conditions and the seasonality of GBS, could "have a meaningful impact on the analysis," according to meeting materials shared by a company spokesperson.
The drugmaker will conduct four different safety studies that will shine light on “the incidence and risk factors of GBS,” Mehta added in the meeting materials.
GSK concurs that the current data come with “limitations and uncertainty” and that more information is needed. The company pledged to start a controlled epidemiological study to evaluate the GBS link and is currently developing the protocol for the study, a spokesperson said in an emailed statement.
“Patient safety is our highest priority, and we will continue to monitor diligently all safety data reported in the ongoing RSV older adult clinical trials and in post-marketing pharmacovigilance systems,” the spokesperson noted.