Thrombosis of inferior mesenteric and splenic vein/Severe Abdominal pain; Thrombosis of inferior mesenteric and splenic vein/ severe abdominal pain; Headache; Nausea; This spontaneous case was reported by a nurse (subsequently medically confirmed) and describes the occurrence of SPLENIC VEIN THROMBOSIS (Thrombosis of inferior mesenteric and splenic vein/ severe abdominal pain) and MESENTERIC VEIN THROMBOSIS (Thrombosis of inferior mesenteric and splenic vein/Severe Abdominal pain) in a 59-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 025L20A and 011B21A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     The patient's past medical history included No adverse event (No recorded medical history).   On 22-Dec-2020, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 19-Jan-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 19-Jan-2021, the patient experienced HEADACHE (Headache) and NAUSEA (Nausea). On 27-Jan-2021, the patient experienced SPLENIC VEIN THROMBOSIS (Thrombosis of inferior mesenteric and splenic vein/ severe abdominal pain) (seriousness criteria hospitalization prolonged and medically significant) and MESENTERIC VEIN THROMBOSIS (Thrombosis of inferior mesenteric and splenic vein/Severe Abdominal pain) (seriousness criteria hospitalization and medically significant). The patient was hospitalized for 1 day due to SPLENIC VEIN THROMBOSIS. At the time of the report, SPLENIC VEIN THROMBOSIS (Thrombosis of inferior mesenteric and splenic vein/ severe abdominal pain), MESENTERIC VEIN THROMBOSIS (Thrombosis of inferior mesenteric and splenic vein/Severe Abdominal pain), HEADACHE (Headache) and NAUSEA (Nausea) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 27-Jan-2021, Computerised tomogram: thrombosis of inferior mesenteric and splenic vein (abnormal) Thrombosis of inferior mesenteric and Splenic vein.     For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter did not provide any causality assessments.   Concomitant product use was not provided by the reporter.  The patient experienced severe abdominal pain and went to Emergency room and CT Scan and lab investigations were done. She was given. The patient stayed for 24 hours in Emergency room. The patient received 1st dose of Moderna vaccine on 22 Dec2021 and no symptom after vaccine administration.  Treatment for the event included prescribed apixaban for 6 months and heparin.  The patient received both scheduled doses of mRNA-1273 prior to the event; therefore, action taken with the drug in response to the event is not applicable.  Company Comment: Based on the current available information and temporal association between the use of the product and the start dates of the events, a causal relationship cannot be excluded.; Sender's Comments: Based on the current available information and temporal association between the use of the product and the start dates of the events, a causal relationship cannot be excluded.