Randomized Controlled Trial
Study population and setting
This analysis combined the safety results from publicly available data from the Pfizer-BioNTech and Moderna vaccine trials, which when combined have over 40,000 vaccine arm recipients. Bell’s palsy events, a condition that causes a temporary weakness or paralysis of the muscles in the face resulting in drooping or stiffening of one side of the face which usually self-resolves, were collected over a median of 2 months post vaccination.
Summary of Main Findings
7 cases of Bell’s palsy were detected in the vaccine recipients compared to 1 in placebo recipients, which translated to an incidence of 104 per 100,000 person-years in vaccinees and 15 per 100,000 person-years in placebo recipients, i.e., an estimated possible 7-fold higher rate in vaccinees, but this difference was not statistically significant. The incidence of Bell’s palsy in the general population is estimated to be between 15 to 30 cases per 100 000 person-years, indicating the rate of Bell’s palsy in the placebo arm was as expected, but the rate in vaccinees was potentially higher than expected.
This report combines data from two large placebo-controlled clinical trials in which participants were carefully followed after immunization, so it is unlikely that events were missed, and the likelihood of misclassifying the event was low. Individually, and even combined, the trials did not have adequate sample size to rule out that the possibility that the higher rate in vaccinees was due to chance. However, the findings for both the Pfizer and the Moderna mRNA COVID vaccines, as well as a review of the risk of Bell’s palsy for other vaccines, namely influenza and meningococcal vaccines, which found excess risk in vaccinees in 5 of 6 studies examined, providing added support for their finding.
No details on the duration and recovery status were provided nor was there a description of the characteristics of participants who experienced the event.
This re-analysis combined rare safety event data from two high-quality COVID vaccine trials to provide a more robust picture of the risk of Bell’s palsy. It also contextualized the findings with respect to risk observed with other vaccines and the background rate in the general population.