Risk and characteristics of Bell’s palsy in adults as an adverse event following COVID-19 vaccination: a retrospective study

Background: Although an association between COVID-19 vaccination and Bell’s palsy (BP) has been reported, a clear causal relationship has not been elucidated. We investigated the risk and clinical characteristics of BP after COVID-19 vaccination. Methods: This retrospective chart review evaluated the association between COVID-19 vaccination and BP by comparing the number of patients diagnosed with BP during the pre-COVID-19 vaccination period (March 2018–February 2021) and the COVID-19 mass vaccination period (March 2021–February 2022). We then compared vaccine-related (time between vaccination and BP onset < 42 days) and -unrelated (time interval ≥ 42 days or non-vaccination) clinical characteristics in newly diagnosed patients with BP. Results: BP occurred more during the COVID-19 vaccination period than in the previous three pre-vaccination years. Thirteen patients developed BP within 42 days of vaccination. All patients, except one, developed BP after mRNA-based vaccination, with most cases (9/13, 69.2%) occurring after the second or third dose. Thirteen patients with vaccine-related BP were younger (age 43.92 ± 13.14 vs. 54.32 ± 16.01 years; p = 0.033) and more frequently experienced taste changes (58.8% vs. 10.9%; p = 0.002) than 52 patients with vaccine-unrelated BP. Patients with vaccine-related BP had a greater likelihood of good and faster (p = 0.042) facial nerve function recovery than those with vaccine-unrelated BP (100% vs. 78%). Conclusion: COVID-19 vaccines, especially mRNA-based vaccines, may be associated with BP cases with distinctive clinical characteristics, which occur more frequently in young individuals, are frequently accompanied by taste changes, and have fast and good recovery.