The observed incidence of Bell’s palsy in the vaccine arms is between 3·5-times and 7-times higher than would be expected in the general population.
Bell’s palsy and SARS-CoV-2 vaccines
Ozonoff, A., Nanishi E., Levy, O. (2021) Bell’s palsy and SARS-CoV-2 vaccines. Lancet Infectious Disease 2021
Published Online February 24, 2021 https://doi.org/10.1016/S1473-3099(21)00076-1
Media reports have stated that the incidence of Bell’s palsy among participants of the Pfizer-BioNTech and Moderna vaccine trials is comparable to that observed in the general population. The FDA briefing on the Pfizer-BioNTech trial stated “observed frequency of reported Bell’s palsy in the vaccine group is consistent with the expected background rate in the general population”, although this statement was removed from the subsequent FDA briefing on the Moderna trial. However, this reporting is based on a misconception, driven by a subtle distinction between rates and proportions, that has persisted in the lay media. The estimated incidence rate of Bell’s palsy in the general population ranges from 15 to 30 cases per 100 000 person-years. Since the 40 000 vaccine arm participants were followed for a median of 2 months, the combined safety population receiving vaccine across the two trials represents roughly 6700 person-years of observation time for an expected incidence of Bell’s palsy of one to two cases, in line with the single observed case in the combined placebo arms. Therefore, the observed incidence of Bell’s palsy in the vaccine arms is between 3·5-times and 7-times higher than would be expected in the general population. This finding signals a potential safety phenomenon and suggests inaccurate reporting of basic epidemiological context to the public.