Ascending paralysis/Flaccid paralysis/Lost his ability to protect his airway; This spontaneous case was reported by a consumer and describes the occurrence of GUILLAIN-BARRE SYNDROME (Ascending paralysis/Flaccid paralysis/Lost his ability to protect his airway) in a 21-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 prophylaxis.     No Medical History information was reported.    On an unknown date, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On an unknown date, the patient experienced GUILLAIN-BARRE SYNDROME (Ascending paralysis/Flaccid paralysis/Lost his ability to protect his airway) (seriousness criteria medically significant and life threatening). At the time of the report, GUILLAIN-BARRE SYNDROME (Ascending paralysis/Flaccid paralysis/Lost his ability to protect his airway) outcome was unknown.        The action taken with mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown) was unknown.       Concomitant medication was not reported.  Patient received first dose of Moderna vaccine in March and subsequently began to experience ascending paralysis. Patient's condition was rapidly escalated requiring intubation and mechanical ventilation. Patient was treated for Guillain-Barre Syndrome. Patient had flaccid paralysis and lost ability to protect airway. Patient would likely need a tracheostomy to allow air to enter the lungs via a tube.  This case was identified as part of a retrospective clean-up activity where certain emails received in the Moderna mailbox were missed to be booked-in.  Company comment: This spontaneous case concerns a 21-year-old male patient, with no reported medical history, who experienced the unexpected serious (medically significant and life-threatening) AESI Guillain-Barre syndrome after receiving the 1st dose of mRNA-1273 vaccine on an unknown date. Patient began experiencing ascending paralysis nine days post vaccination. Condition progressed to flaccid paralysis and loss ability to protect airway requiring intubation and mechanical ventilation. Patient was treated for Guillain-Barre syndrome. It was reported that patient would likely need a tracheostomy. Clinical course and treatment details were not reported. The outcome of event was unknown. The benefit-risk relationship of mRNA-1273 is not affected by this report. Event assessed as serious based on medical judgement.; Sender's Comments: This spontaneous case concerns a 21-year-old male patient, with no reported medical history, who experienced the unexpected serious (medically significant and life-threatening) AESI Guillain-Barre syndrome after receiving the 1st dose of mRNA-1273 vaccine on an unknown date. Patient began experiencing ascending paralysis nine days post vaccination. Condition progressed to flaccid paralysis and loss ability to protect airway requiring intubation and mechanical ventilation. Patient was treated for Guillain-Barre syndrome. It was reported that patient would likely need a tracheostomy. Clinical course and treatment details were not reported. The outcome of event was unknown. The benefit-risk relationship of mRNA-1273 is not affected by this report. Event assessed as serious based on medical judgement.