Incomplete Bell's Palsy; Right facial nerve paresis; Possible underlying immunologic reaction; This literature case  was received on 10-Apr-2023, reported by a physician and concerned a 7-month-old, male patient.   The aim of this literature brief report was presentation of 7-month-old male patient who experienced incomplete Bell's palsy following influenza vaccination.   The patient had no relevant medical history and was not taking any concomitant medications. The patient had not traveled recently, and family history was negative for any neurological, bleeding, or clotting disorders.  On an unspecified date (at his 6-month well-child visit, as reported), the patient was vaccinated with influenza vaccine (reported as 'inactive quadrivalent influenza vaccine') (brand not specified; route of administration: intramuscular, dose, anatomical location and indication: not reported). The batch number was not reported.   On an unspecified date, the patient was vaccinated with booster dose of influenza vaccine (reported as 'inactive quadrivalent influenza vaccine') (brand not specified; route of administration: intramuscular, dose, anatomical location and indication: not reported). The batch number was not reported.  On an unspecified date, six days after receiving influenza vaccine, the patient, described as a previously healthy developmentally typical 7-month-old male, was presented to the emergency department with acute onset right-sided facial weakness that the patient's parents first noticed earlier in the morning. The patient's exam was notable for subtle right nasolabial fold flattening and drooping of the right corner of his mouth. The patient was able to close both eyelids completely and lift both eyebrows. Magnetic resonance imaging (MRI) of the brain was performed due to concern for supranuclear involvement of the facial nerve in the setting of bilateral preserved forehead movements. The MRI demonstrated slight asymmetric increase in enhancement of the tympanic and mastoid segments of the right facial nerve. Labs were notable for a negative severe acute respiratory syndrome coronavirus 2 (SARSCoV-2) polymerase chain reaction (PCR) and a negative serum herpes simplex virus (HSV) 1/2 PCR. The patient was not evaluated for Lyme disease, given the absence of erythema migrans by history and exam. The patient had no known exposure to any ticks, especially those from a Lyme endemic region. The patient was discharged home with a diagnosis of right facial nerve paresis. It was reported that the patient possibly had an underlying immunologic reaction and incomplete Bell's palsy.  On an unspecified date, the patient was evaluated by both pediatrician and a pediatric neurologist following discharge.  On an unspecified date, the patient recovered from all events. As reported, the patient had complete resolution of the facial nerve paresis within 48 hours of symptom onset. The patient had not had further recurrence of symptoms even with continued yearly influenza immunizations and continued to grow and develop normally.  In conclusion, depending on the branches and degree of facial nerve involvement, Bell's palsy could be presented as a spectrum ranging from partial weakness to a complete paralysis. The variable physical exam findings could make determining infranuclear from supranuclear etiologies more challenging. Findings may be more subtle in the pediatric population as patients may be unable to report subjective sensory changes. Although Bell's palsy had been described as having a clear temporal association with influenza immunization in adults, this phenomenon had not been previously well-documented or reported in the pediatric population and further studies are needed. Given the disease burden of influenza and the proven safety record of influenza vaccines, physicians should continue to strongly encourage influenza immunization for all children 6 months and older.  The reporter assessed the events to be possibly related to influenza vaccine. As reported, although not conclusive, the close temporal association between the patient's recent inactivated quadrivalent influenza vaccine and onset of facial nerve paresis suggested a possible underlying immunologic reaction.  The event of 'Bell's palsy' was considered to be medically significant by a Physician within Seqirus's Pharmacovigilance and Risk Management Department.   Company comment: A 7-month-old patient was presented to the emergency department with acute onset right-sided facial weakness six days after receiving the suspect product influenza vaccine. The patient's exam was notable for subtle right nasolabial fold flattening and drooping of the right corner of his mouth. The patient was able to close both eyelids completely and lift both eyebrows. Magnetic resonance imaging of the brain was performed due to concern for supranuclear involvement of the facial nerve in the setting of bilateral preserved forehead movements and demonstrated slight asymmetric increase in enhancement of the tympanic and mastoid segments of the right facial nerve. The patient was discharged home with a diagnosis of right facial nerve paresis. It was reported that the patient possibly had an underlying immunologic reaction and incomplete Bell's palsy. The patient had no relevant medical history and was not taking any concomitant medications. Based on plausible temporal relationship, causality for the events right facial nerve paresis, Bell's palsy, and immunisation reaction is assessed as possibly related.; Reporter's Comments: As reported, although not conclusive, the close temporal association between the patient's recent inactivated quadrivalent influenza vaccine and onset of facial nerve paresis suggested a possible underlying immunologic reaction.; Sender's Comments: A 7-month-old patient was presented to the emergency department with acute onset right-sided facial weakness six days after receiving the suspect product influenza vaccine. The patient's exam was notable for subtle right nasolabial fold flattening and drooping of the right corner of his mouth. The patient was able to close both eyelids completely and lift both eyebrows. Magnetic resonance imaging of the brain was performed due to concern for supranuclear involvement of the facial nerve in the setting of bilateral preserved forehead movements and demonstrated slight asymmetric increase in enhancement of the tympanic and mastoid segments of the right facial nerve. The patient was discharged home with a diagnosis of right facial nerve paresis. It was reported that the patient possibly had an underlying immunologic reaction and incomplete Bell's palsy. The patient had no relevant medical history and was not taking any concomitant medications. Based on plausible temporal relationship, causality for the events right facial nerve paresis, Bell's palsy, and immunisation reaction is assessed as possibly related.