Hyperpigmentation; Sloughed skin; Bullous eruption eventually peeled off with "sloughed skin"; Redness down to side of the arm and demarcation, looks like a burn; Constant burning sensation; Bullous eruption on her arm; Bruising; Discoloration; Blisters; Vesicular pustules; Significant pruritus; Arm felt warm; Significant tenderness and pain on arm/significant tenderness and pain; Her arm felt warm, painful and was red; Swelling extended down to her arm; A spontaneous report was received from a physician, who was also a 63-year old, female, patient who received Moderna's COVID-19 vaccine (mRNA-1273) and experienced, bullous eruption on her arm, bruising, discoloration, blisters, vesicular pustules, significant pruritus, hyperpigmentation, constant burning sensation, sloughed skin, arm felt warm, bullous eruption eventually peeled off with "sloughed skin," redness down to side of the arm and demarcation, looks like a burn, significant tenderness and pain on arm/significant tenderness and pain, her arm felt warm, painful and was red, and swelling extended down to her arm.  The patient's medical history, as provided by the reporter, included hypertension, sulfonamide drug allergy, and penicillin drug allergy. Concomitant medications reported included bisoprolol, telmisartan, vitamin D, vitamin C, and zinc.   On 30 Dec 2020, approximately four hours prior to the onset of the events, the patient received their first of two planned doses of mRNA-1273 (Lot Number: 025J20A) intramuscularly for prophylaxis of COVID-19 infection.   On 30 Dec 2020, after receiving the vaccine, the patient experienced warmth, redness, and pain in the arm which she treated with ice and diphenhydramine.  On 31st Dec 2020, 14 hours after vaccine administration, the patient started to experience bullous eruption on her arm, pruritis and constant burning sensation in the arm. She reported having swelling extended down to her arm, bruising, discoloration, blisters, small vesicular pustules, erythema down to the side of the arm, and demarcation. She spoke to her primary care provider as her rash continued to evolve. She was started on a methylprednisolone pack but only took two doses for concern it would blunt the immune response to the vaccine. Additionally, she was treated with triamcinolone ointment.  On 03 Jan 2021, the bullous eruptions peeled off with sloughed skin, she had an excoriated area underneath the skin. She also had tenderness and pain in the arm which resolved spontaneously. The patient self-treated the events with benzethonium chloride and vitamin E oil.  On 28th Jan 2021, the patient had hyperpigmentation of her posterior arm with an excoriated area.   Action taken with mRNA-1273 in response to the events was not reported.   The outcome of the events, bullous eruption on her arm, bruising, discoloration, blisters, vesicular pustules, significant pruritus, hyperpigmentation, constant burning sensation, arm felt warm, bullous eruption eventually peeled off with "sloughed skin", redness down to side of the arm and demarcation, looks like a burn, her arm felt warm, painful and was red, and swelling extended down to her arm, was not reported. The outcome of the event, sloughed skin, was considered recovering. The outcome of the events, significant tenderness and pain on arm/significant tenderness and pain and swelling extended down to her arm, was considered resolved.; Reporter's Comments: This case concerns a 63 year old female patient with medical history of hypertension, sulfonamide drug allergy, and penicillin drug allergy, who experienced a serious unexpected event of Dermatitis bullous and NS unexpected events of bruising, discoloration, blisters, vesicular pustules, significant pruritus, hyperpigmentation, constant burning sensation, sloughed skin and arm felt warm. The events occurred 14 hours after first dose of the study medication administration. She was started with a methylprednisolone pack and triamcinolone ointment.  Based on the current available information and temporal association between the use of the product and the start date of the event, a causal relationship cannot be excluded.