CDC and FDA have committed to monitoring recipients of two COVID-19 vaccines for Bell’s palsy, a type of facial paralysis.
FDA, however, concluded that there is insufficient data to determine whether the mRNA-based vaccines from Moderna (NSDQ:MRNA) and Pfizer (NYSE:PFE)/BioNTech (NSDQ:BNTX) are linked to the condition, which is often temporary.
Both vaccines use messenger RNA technology, which is novel for vaccines.
In Phase 3 clinical trials from Pfizer-BioNTech and Moderna, a handful of patients developed the condition. Four patients in the vaccine arm of the Pfizer-BioNTech trial developed Bell’s palsy and none in the placebo group. Three patients in the Moderna trial’s vaccine arm developed the condition, and one in the placebo arm.
“We don’t know really if these Bell’s palsy [cases] ended up happening coincidentally in the vaccine group. We’ll have to see,” said Abinash Virk, an infectious disease specialist at the Mayo Clinic, last week before FDA released its assessment of the Moderna Phase 3 trial.
A limited number of COVID-19 patients have developed Bell’s palsy as well.
An FDA briefing document for Moderna’s vaccine stated that one case in the vaccine group was a serious adverse event. A “67-year-old female with diabetes was hospitalized for stroke due to new facial paralysis 32 days after vaccination,” according to the report. “This case was reported as resolving,” it continued.
The Bell’s palsy cases in the Pfizer-BioNTech and Moderna trials will “create some ongoing discussion,” concluded a briefing note from UBS analysts Navin Jacob and Dr. Jonathan Lim.
But some degree of Bell’s palsy would be expected in a large clinical trial, according to UBS. The background rate of the condition in the general population is 25 to 35 per 100,000 people, which would imply eight to 12 cases across the Pfizer-BioNTech and Moderna trials, which involved approximately 44,000 and 30,000 participants, respectively. There were a total of eight Bell’s palsy cases across both trials.
While the cause of Bell’s palsy is unclear, reactivation of a dormant viral infection could be the principal cause of the disorder, according to the NIH. Reactivation of herpes simplex virus may be the most common cause. Pregnancy and diabetes can increase the risk of the condition.
Researchers have linked Bell’s palsy to other vaccine studies. In Switzerland, health authorities pulled an inactivated intranasal flu vaccine linked to the condition from the market in the early 2000s. One study conservatively estimated that recipients of that vaccine were 19 times more likely to develop Bell’s palsy than the general population.
FDA researched similar conclusions about the situation in its briefing documents for the Pfizer-BioNTech and Moderna vaccines. “Considering the temporal association and biological plausibility, a potential contribution of the vaccine to the manifestations of these events of facial palsy cannot be ruled out,” the agency concluded in its notes on the Moderna vaccine. The agency is recommending surveillance for Bell’s palsy as both vaccines reach the public.
FDA authorized the Pfizer-BioNTech vaccine last week. It could authorize the Moderna vaccine as soon as Dec. 18.