multisystemic inflammatory syndrome (MIS-A); This literature-non-study case was reported in a literature article and describes the occurrence of MULTISYSTEM INFLAMMATORY SYNDROME IN ADULTS (multisystemic inflammatory syndrome (MIS-A)) in a 73-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination.   LITERATURE REFERENCE:    Concurrent medical conditions included Diabetes, Atrial fibrillation, Hypertension and Hyperlipidemia.    On an unknown date, the patient received dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On an unknown date, the patient experienced MULTISYSTEM INFLAMMATORY SYNDROME IN ADULTS (multisystemic inflammatory syndrome (MIS-A)) (seriousness criteria hospitalization and medically significant). The patient was treated with DESMOPRESSIN ACETATE (DESMOPRESSIN [DESMOPRESSIN ACETATE]) for Hyponatremia, at an unspecified dose and frequency. At the time of the report, MULTISYSTEM INFLAMMATORY SYNDROME IN ADULTS (multisystemic inflammatory syndrome (MIS-A)) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Alanine aminotransferase: 84 iu/l 84 IU/L. On an unknown date, Aspartate aminotransferase: 116 iu/l 116 IU/L. On an unknown date, Blood culture: negative (Negative) Negative. On an unknown date, Blood smear test: abnormal (abnormal) showed normocytic anemia, neutrophilia, monocytosis, lymphopenia,and thrombocytosis. On an unknown date, Blood sodium: 120 mmol/l 120 mmol/L. On an unknown date, Chest X-ray: normal (normal) Chest x-ray did not show pleural effusion, consolidation or pneumothorax. On an unknown date, Culture urine: negative (Negative) Negative. On an unknown date, SARS-CoV-2 test: negative (Negative) COVID-19 antigen was negative and negative (Negative) COVID-19 PCR Test was negative. On an unknown date, Ultrasound liver: ruled out cirrhosis Liver ultrasound ruled out cirrhosis. On an unknown date, White blood cell count: 35.16 k/mul 35.16 K/muL, elevated white blood cell count and 14.42 k/mul discharged 18 days later with WBC of 14.42 K/muL.     The action taken with mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown) was unknown.   For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter considered MULTISYSTEM INFLAMMATORY SYNDROME IN ADULTS (multisystemic inflammatory syndrome (MIS-A)) to be related.    Patient had no prior history of COVID infection.  Patient presented to the Emergency Department secondary to an elevated white blood cell count.  Patient started with weakness, low appetite, fever, chills, and headaches 2 days after receiving the Moderna vaccine and was hemodynamically stable and afebrile. Patient denied having unintentional weight loss, fever, adenopathy, rash, pruritus, new medications, or recent infection.  Patient was started on broad spectrum antibiotics, and on hypertonic saline, fluid restriction for severe hyponatremia.  Laboratory tests included hepatitis panel test which was negative and workup for myeloproliferative process including Jak2, CALR, MPL, BCR -ABL, was also negative.  Patient was briefly transferred to ICU secondary to worsening hyponatremia, decreased mental status, and acute kidney injury(AKI). Patient developed erythematous non-pruritic rash on his arms and upper chest on day 13 which resolved after oral antihistamines. Transaminitis, hyponatremia, and AKI resolved, and patient was discharged 18 days later.  This is a Literature-Non-Study case concerning a 73-year-old male patient, with no relevant medical history who experienced the serious (hospitalized and medically significant), unexpected AESI of Multisystem inflammatory syndrome in adults on an unknown date, approximately 2 days after the administration of a dose of the mRNA-1273 vaccine. Testing sowed neutropenia, monocytosis, leukopenia, thrombocytosis, hyponatremia, increased liver enzymes and elevated WBC along with normal hepatitis screen, CXR and ultrasound of the liver. Treatment was with desmopressin and antihistamines. The event is resolving. The benefit-risk relationship of the mRNA-1273 vaccine is not affected by this report.   Most recent FOLLOW-UP information incorporated above includes: On 01-Mar-2022: Significant FU: Follow up received by safety on 02-Mar-2022 has Email from team and contains significant information. Citation details updated (additional authors name and publication year) and onset latency added; Sender's Comments: This is a Literature-Non-Study case concerning a 73-year-old male patient, with no relevant medical history who experienced the serious (hospitalized and medically significant), unexpected AESI of Multisystem inflammatory syndrome in adults on an unknown date, approximately 2 days after the administration of a dose of the mRNA-1273 vaccine. Testing sowed neutropenia, monocytosis, leukopenia, thrombocytosis, hyponatremia, increased liver enzymes and elevated WBC along with normal hepatitis screen, CXR and ultrasound of the liver. Treatment was with desmopressin and antihistamines. The event is resolving. The benefit-risk relationship of the mRNA-1273 vaccine is not affected by this report.