Two people who received Pfizer’s respiratory syncytial virus (RSV) vaccine during a clinical trial were later diagnosed with Guillain-Barre syndrome, and the U.S. Food and Drug Administration has asked Pfizer to conduct a safety study if the injection is used. approved, released Friday according to agency documents.
The cases were confirmed in two adults in their 60s who were among 20,000 vaccine recipients in Pfizer’s phase 3 clinical trial. One person’s illness cleared completely after three months, and another improved after six months. There were no cases of Guillain-Barre among people who did not get the shot.
“Given the temporal association and biological plausibility, the FDA agrees with the investigators’ assessments that these events may have been related to the study vaccine. … Therefore, [Guillain-Barre] is considered an important potential risk,” the FDA says in the documents, which were released ahead of a meeting of its independent vaccine advisors, the Vaccines and Related Biological Products Advisory Committee, on Tuesday and Wednesday.
The committee is scheduled to discuss and make recommendations on RSV vaccines for adults age 60 and older from Pfizer and GSK.
Guillain-Barre syndrome is a rare neurological disorder in which the immune system attacks its own nerves, causing muscle weakness and sometimes paralysis. While most people make a full recovery, some cases can be fatal or have lasting consequences.
The incidence of Guillain-Barre is approximately 1.5 to 3 cases for 100,000 adults over age 60 in the US annually, according to the FDA.
“Given the higher than background rate of GBS observed in the Phase 3 trial, the FDA will recommend a post-marketing study and enhanced surveillance for further evaluation of GBS and other immune-mediated demyelinating disorders in post-marketing use,” the FDA says.
In a briefing paper submitted for next week’s meetings, Pfizer says the cases have other possible explanations and that its injection is a “well-tolerated and safe vaccine, with a favorable benefit-risk ratio.” The company says it will conduct a safety study on Guillain-Barre syndrome if the RSV injection is approved.
RSV is a highly contagious virus that causes a flu-like illness in people of all ages that increases in severity with age. According to the U.S. Centers for Disease Control and Prevention, RSV is responsible for an estimated 177,000 hospitalizations and 14,000 deaths each year among adults age 65 or older.
There are no vaccines approved for immunization against RSV in children or adults.
The Pfizer vaccine was 66.7% effective in preventing moderate lower respiratory tract disease with two or more symptoms and 85.7% effective in preventing major illness, the FDA filings said.
GSK’s RSV vaccine candidate for older adults was 83.5% effective in preventing serious lower respiratory tract disease. The company also reported a possible case of Guillain-Barré syndrome among recipients of the vaccine, but said there was not enough evidence to confirm a diagnosis. The FDA considers the case related to the vaccine and said it will review GSK’s safety plan.
Data from both vaccines were discussed Thursday at a meeting of the CDC’s Advisory Committee on Immunization Practices. The working group concluded that the vaccines “showed significant efficacy against lower respiratory tract disease caused by RSV in older adults”, but that “post-licensing surveillance for both the safety and effectiveness of the vaccine will be critical” if the vaccines are approved by the FDA.