RECTAL BLEEDING; PERICARDITIS; This 57-year-old, female subject was participating in a study and experienced the life-threatening adverse event of special interest (AESI) pericarditis and rectal bleeding.  The subject's medical history, as provided by the investigator, included liver transplant, hyperlipidemia, hypertension, anemia due to chronic kidney disease, intermittent hypomagnesemia, depression, anxiety, menopause, chronic low back pain, non-ST myocardial infarction, intermittent hyperkalemia, insomnia, bilateral sensory peripheral neuropathy in lower extremities, non-alcoholic cirrhosis, dry eyes, left subclavian artery stenosis, asthma, herpes simplex virus (HSV)-1 infection, Crohn disease, vitamin B12 deficiency, type 2 diabetes mellitus, end stage renal disease, gastroesophageal reflux disease, and cavernoma. Concomitant medications reported included amlodipine, lidocaine, paracetamol, lisinopril, trazodone, ticagrelor, tacrolimus, sevelamer carbonate, pregabalin, labetalol, ciclosporin, buspirone, duloxetine, venlafaxine hydrochloride, acetylsalicylic acid, folic acid, vitamin B12, salbutamol, valaciclovir hydrochloride, ergocalciferol, torasemide, epoetin zeta, rosuvastatin calcium, pantoprazole sodium sesquihydrate, fenofibrate, melatonin, sodium bicarbonate, pantoprazole, furosemide, insulin porcine, dextrose, colestyramine, insulin aspart, and isosorbide mononitrate.  The subject previously experienced the SAE of pneumonia (MOD-2021-415676), SAEs of syncope, symptomatic covid-19 infection, fall (MOD-2022-444391), SAE of pulmonary edema (MOD-2022-486233), SAE of Dieulafoy's lesion (MOD-2022-501812), SAE of worsening intermittent hyperkalemia (MOD-2022-521334), SAE of hyperkalemia (MOD-2022-583458) SAE of transaminitis (MOD-2022-583460), and the SAE of worsening hyperkalemia (MOD-2022-589838).  Prior to event onset, the subject received intramuscular mRNA-1273 (Dose 1) for SARS-CoV-2 vaccination on 19 Nov 2021, approximately 6 months 22 days before onset of the events.  On 23 Mar 2022, colonoscopy showed external and internal hemorrhoids, end-to-end ileo-colonic anastomosis with mild stenosis with pseudopolyps; biopsies were obtained and were normal.  On 09 Jun 2022, the subject developed rectal bleeding. She went to the emergency department with one day of acute onset worsening sharp epigastric pain radiating to the back associated with mild nausea and multiple episodes of bright red blood with bowel movements. She endorsed chronic diarrhea but denied fevers, chills, chest pain, dyspnea, vomiting, urinary symptoms, headache, lightheadedness, dizziness, neck pain or stiffness, or trauma. She did not complete dialysis that day. She received morphine in the emergency department. She endorsed nausea, melena, rebound tenderness, and bright red blood per rectum. White blood cell count (WBC) was elevated at 17.2, lactic 1.6, potassium 5.6. She denied fevers and chills. Her last hemodialysis was a full session performed two days prior. Computerized tomography scan (CT) of the abdomen and pelvis with contrast showed multifocal colitis, likely representing an acute flare of known Crohn's disease, with evidence of a fistula adjacent to the neoterminal ileum. There was a small amount of free intraperitoneal fluid without organized collection. Findings in the lung bases were suggestive of mild pulmonary edema. The subject was admitted to the hospital.  On 10 Jun 2022, a flexible sigmoidoscopy showed continuous sigmoid ulceration and inflammation with rectal sparing. Sigmoid colon tissue biopsy showed sigmoid colonic mucosa with features of ischemic colitis. Clostridium difficile was negative, C-reactive protein was elevated at 170. There were no signs of tamponade or pulmonary effusions on ultrasound.  On 13 Jun 2022, the subject was tolerating a full diet well.  On 14 Jun 2022, computerized tomography angiography (CTA) of the abdomen and pelvis showed severe celiac stenosis with superior mesenteric artery (SMA) collateralization, rectosigmoid and distal ileum edema with fistulous tracking secondary to Crohn's disease, increased bibasilar atelectasis and ground glass opacities (likely edema), small-moderate pericardial effusion. Vascular surgery was consulted for celiac stenosis, who recommended no acute intervention but did recommend outpatient follow up.  On 15 Jun 2022, computerized tomogram (CT) of the abdomen and pelvis showed worsening pericardial effusions.  On 19 Jun 2022, the subject experienced pericarditis that had complicated her admission for gastrointestinal bleed. She'd had worsening chest pain, shortness of breath x3 days, right upper quadrant pain, elevated lactate and WBC.  On 22 Jun 2022, chest x-ray showed possible right lower lobe infiltrate/effusion.  No action was taken with the study drug in response to the events.   The events, rectal bleeding and pericarditis, were reported as not resolved.  The investigator assessed the event, rectal bleeding, as not related to study drug and not related to study procedure. The investigator assessed the event, pericarditis, as not applicable to study drug and not applicable to study procedure.  Follow-up received on 22 Jun 2022 included additional event term, concomitant medications, updated severity for event rectal bleeding (previously moderate), and diagnostic/laboratory test results.  Company comment: This case concerns a 57-year-old, female subject with a medical history of liver transplant ( due to non-alcoholic cirrhosis), hyperlipidemia, hypertension, anemia due to chronic kidney disease, intermittent hypomagnesemia, depression, anxiety, non-ST myocardial infarction, intermittent hyperkalemia, bilateral sensory peripheral neuropathy in lower extremities, asthma, Crohn disease, type 2 diabetes mellitus, end stage renal disease, gastroesophageal reflux disease, and cavernoma, among others, who experienced the unlisted event of rectal bleeding and life-threatening adverse event of special interest (AESI) pericarditis. The event rectal bleeding occurred 6 months 22 days after the mRNA-1273 administration (1 dose), and the event pericarditis occurred 7 months 2 day after mRNA-1273 administration (1 dose). The events, rectal bleeding and pericarditis, were reported as not resolved. The event rectal bleeding was considered unrelated to IP in agreement with the Investigator due to long latency and lack of biological plausibility. The event rectal bleeding might be explained by underlying Crohn´s disease. The investigator assessed the event, pericarditis, as not applicable to study drug and not applicable to study procedure. The sponsor considered the event as not related to the study vaccine due to long latency. Additional information was requested.; Reporter's Comments: This case concerns a 57-year-old, female subject with a medical history of liver transplant ( due to non-alcoholic cirrhosis), hyperlipidemia, hypertension, anemia due to chronic kidney disease, intermittent hypomagnesemia, depression, anxiety, non-ST myocardial infarction, intermittent hyperkalemia, bilateral sensory peripheral neuropathy in lower extremities, asthma, Crohn disease, type 2 diabetes mellitus, end stage renal disease, gastroesophageal reflux disease, and cavernoma, among others, who experienced the unlisted event of rectal bleeding and life-threatening adverse event of special interest (AESI) pericarditis. The event rectal bleeding occurred 6 months 22 days after the mRNA-1273 administration (1 dose), and the event pericarditis occurred 7 months 2 day after mRNA-1273 administration (1 dose). The events, rectal bleeding and pericarditis, were reported as not resolved. The event rectal bleeding was considered unrelated to IP in agreement with the Investigator due to long latency and lack of biological plausibility. The event rectal bleeding might be explained by underlying Crohn´s disease. The investigator assessed the event, pericarditis, as not applicable to study drug and not applicable to study procedure. The sponsor considered the event as not related to the study vaccine due to long latency. Additional information was requested.