Severe allergic reaction; anaphylactic reaction; A spontaneous report was received from a physician, who was also a male patient who received Moderna's COVID-19 Vaccine and developed a severe/anaphylactic allergic reaction.  The patient's medical history, as provided by the reporter, included a shellfish allergy and elevated Immunoglobulin E. He reported no history of adverse events following other immunizations, that all his immunizations were up to date, and that he gets the flu shot annually. Products known to have been used by the patient, within two weeks prior to the event, included pantoprazole, vitamin D, and vitamin B12.  On 24 Dec 2020, minutes prior to the onset of the event, the patient received the first of two planned doses of mRNA-1273 intramuscularly for COVID-19 infection prophylaxis.  Within minutes, the patient felt dizzy and his heart was racing. His throat felt swollen and he experienced shortness of breath ("heavy breathing") with no wheezing or stridor, but with chest tightness that he felt was possibly related to anxiety about receiving the vaccine and the potential for allergic reaction. No supplemental oxygen was required. Vital signs showed a heart rate of 145, with normal blood pressure (BP) and oxygen saturation. After a few more minutes, he started to feel numbness and tingling in his mouth and tongue. He experienced diaphoresis ("drenched in a cold sweat"), skin pallor ("skin was severely pale"), felt faint, and reported that his blood pressure was undetectable by a monitor. He did not lose consciousness and denied any skin rash. The patient felt he was developing an allergic reaction and self-administered his personal epinephrine auto-injector. He felt better within five to six minutes after self-administration of epinephrine and was taken by stretcher to the Emergency Department for further evaluation and treatment of shortness of breath, dizziness, palpitations, and numbness. The patient was evaluated, treated, observed, and discharged four hours later. Treatment provided for the events while in the Emergency Department included diphenhydramine hydrochloride, intravenous (IV) fluids, IV steroids, and famotidine.  On 25 Dec 2020, the patient felt fully recovered.  On 26 Dec 2020, the patient felt dizzy and reported experiencing a "rapid heart rate" of 70-120 with a systolic BP that was abnormal for him at 150 mmHg. He also reported that he felt premature atrial contractions, for which he took his wife's propranolol. His heart rate came down, but he still felt flushing and dizziness for a few more hours.  Action taken with mRNA-1273 in response to the event was not reported.  The outcome of the event, severe/anaphylactic allergic reaction, was considered resolved on 26 Dec 2020.  The reporter assessed the event of severe/anaphylactic allergic reaction as related to Moderna's COVID-19 Vaccine due to the temporal association and the similarity of symptoms previously experienced with severe/anaphylactic allergic reactions to shellfish.; Reporter's Comments: Company Comment: This case concerns a male patient with medical history of shellfish allergy , who experienced an unexpected events of severe allergic reaction; anaphylactic reaction, dizzy, faint, heart racing, tongue prickled and went numb, cold sweat, blood pressure plummeted, shortness of breath, numbness and skin was pale..The onset of event occurred 15 hrs the first dose of vaccine administration . The events are assessed as possibly related to vaccine.