[Bell's Palsy Secondary to COVID-19 Vaccine Pfizer: Case report].

BACKGROUND: BNT162b2 (Pfizer-BioNTech) is a nucleosidemodified mRNA vaccine formulated with lipid nanoparticles for the prevention of COVID-19 disease caused by SARSCoV-2 infection. In early December 2020, BNT162b2 received an emergency use authorization, initial efficacy and safety data have been released, consumer / patient information sheets for vaccines distributed in North America do not warn of Bell's palsy as a possible adverse effect. We reported the case of a patient who developed Bell's palsy on the right side in less than 3 hours after the application of the first dose of the Pfizer-BioNTech COVID-19 vaccine. CLINICAL CASE: 32-year-old latina woman who developed right facial paralysis after receiving the first dose of the BNT162b2 mRNA vaccine on April 7, 2021; with right facial paresis, absence of forehead wrinkles, lip-buccal sulcus and nasolabial fold; spasms of the facial and periorbital muscles, laterocervical pain; possible etiologies were ruled out, prednisone, gabapentin and topiramate. CT without alterations, achieving gradual improvement; until full functional recovery after 15 days. With benign evolution, congruent with the natural history of the disease, classifying it as idiopathic Bell's palsy. CONCLUSIONS: Although a causal relationship cannot be established, the time and mode of appearance of the paralysis suggested a relationship with the application of the BNT162b2 vaccine. Given the recommendation of the health authorities to monitor the cases of Bell's palsy, and the surveillance of events supposedly attributable to vaccination (ESAVI) and as it is the first case reported in the literature, in the mexican population, we believe that this case should be shared with the scientific community in a timely manner.