Anaphylactic reaction; Massive bloody diarrhea; One large vomitus; A spontaneous report was received from a physician who was also a female patient who received Moderna's COVID-19 vaccine (mRNA-1273) and experienced massive bloody diarrhea, anaphylactic reaction and one large vomitus.  The patient's medical history included hives. No relevant concomitant medications were reported.   On 11 Jan 2021 at 1 p.m., prior to the onset of the events, the patient received their first of two planned doses of mRNA-1273 (Lot Number: 027L20A) intramuscularly or subcutaneously in the left deltoid for prophylaxis of COVID-19 infection.   On 11 Jan 2021, the event began 9 hours later with massive bloody diarrhea from 11 p.m. to 3 p.m. and one large vomitus.  On 12 Jan 2021, the patient experienced hives at 3 a.m. She woke up again because of the hives at 6:30 a.m. Within 15 minutes, hives were all over the place and spread very quickly everywhere but her face. Hives were the worst in the palm of her hands. Treatment included diphenhydramine. Thirty minutes later, she woke up with a beefy red and fat tongue that felt huge and wouldn't fit in roof of her mouth. The patient found it hard to talk and swallow, and her speech was funny. The patient went to the emergency room (ER). At the ER, treatment included intravenous (IV) solumedrol, IV diphenhydramine, IV famotidine, and IV fluids. She reported that it took approximately 2-3 hours for her tongue to feel the right size, and she stayed in the ER for approximately 4 hours.  At home, after seeing her primary care physician, she began taking diphenhydramine, famotidine, oral methylprednisolone, and fexofenadine.  On an undisclosed date, the patient saw an allergist/ immunologist who did bloodwork and an intradermal test for polysorbate; all three times tested was negative. The allergist also did a skin prick test for polyethylene glycol (PEG) allergy, and there was a reaction at full concentration.  On an undisclosed date, the patient's complement level was normal, and her tryptase was elevated which indicated acute inflammatory. Immunoglobulin E level was normal. White blood cell count was 19,000 with no left shift; 48 hours later white blood cell count was 16,000; her physician thought it was due to steroids and stress of a reaction.  On 15 Jan 2021, a COVID antibody test was negative. Complement level was normal, and tryptase was elevated, which indicated acute inflammatory. White blood cell count was 19,000 with no left shift.  Action taken with the second dose of mRNA-1273 in response to the event was not reported.   The outcome for the event, anaphylactic reaction, was not provided. The outcome for the event, massive bloody diarrhea, was considered resolved on 12 Jan 2021. The outcome for the event, one large vomitus, was considered resolved on 11 Jan 2021.; Reporter's Comments: This spontaneous report concerns a female patient with medical history of hives, who experienced serious events of massive bloody diarrhea and anaphylactic reaction and non-serious event of one large vomitus. The events occurred on the same day after the first dose of mRNA-1273 vaccine (Lot Number: 027L20A, expiration date: unknown).  Skin prick test for polyethylene glycol (PEG) showed reaction at full concentration. Treatment included solumedrol, diphenhydramine, famotidine, methylprednisolone and fexofenadine and outcome is resolved. Based on the information provided which include tempral association and evidence of reaction to a constituent of the mRNA-1273 vaccine, Ac causal association between the events and the vaccine administration cannot be excluded.