BIg black thing; Big scar; Felt like chemical burn; Peeling; Cellulitis; Extravasation in tissues; Bruising from upper arm down to elbow; Arm was hot and tender; Swelling from upper arm down to elbow; Arm hot and tender; Bump/clot at injection site; Unsure if it was given intramuscularly; A spontaneous report was received from a physician who was also a 59-year-old female patient, who received Moderna's COVID-19 Vaccine (mRNA-1273) and experienced a bump/clot at the injection site, swelling, bruising from upper arm to elbow, feeling hot, tenderness, extravasation in tissues, vaccination site cellulitis, a big blackened area, scar, chemical burn, unsure whether it was intramuscular and peeling.  The patient's medical history was not provided. Concomitant medication use was not provided by the reporter.   On 23 Dec 2020, immediately prior to the onset of symptoms, the patient received the first of two planned doses of mRNA-1273 (Lot number unknown) intramuscularly in the left arm for prophylaxis of COVID-19 infection. The physician reported that she was injected with the vaccine abruptly and roughly. She noticed a bump at the injection site right away. The nurse applied a cold compress. Later that day, she realized it was a clot.   On 24 Dec 2020, she had swelling, bruising from her upper arm to her elbow, and the area was hot and tender.   On 30 Dec 2020, she went to the emergency room where an ultrasound showed extravasation in the tissues. She was treated with cephalexin for cellulitis.   On 01 Jan 2021, the bump began to subside; however, there was a large black area that started to peel. The reporter stated it looked like a chemical burn.  On an undisclosed date, there was a large scar in its place.   Treatment for the events included a cold compress and cephalexin.    The reporter stated she is unsure whether it was intramuscular.  Action taken with mRNA-1273 in response to the events was not provided.   The event, scar, was not resolved. The outcome of the events, bump/clot at the injection site, swelling, bruising from upper arm to elbow, feeling hot, tenderness, extravasation in tissues, vaccination site cellulitis, a big blackened area, chemical burn, and peeling, were considered resolving. The event, unsure whether is was intramuscular, was resolved.; Reporter's Comments: This report refers to a case of incorrect route of administration for mRNA-1273 and concerns a 59 year-old, female patient, who experienced the events of bump/clot at the injection site, swelling, bruising from upper arm to elbow, feeling hot, tenderness, extravasation in tissues, vaccination site cellulitis, a big blackened area, scar, chemical burn and peeling. The event of bump/clot at the injection site occurred the same day after the first and only dose of mRNA-1273 vaccine administration. The events of swelling, bruising from upper arm to elbow, feeling hot, tenderness occurred the next day after the vaccine administration.  The events of extravasation in tissues, vaccination site cellulitis occurred 7 days after the vaccine administration. The events of a big blackened area, scar, chemical burn and peeling occurred 9 days after the vaccine administration. Based on the current available information and temporal association between the use of the product and the start of the events, a causal relationship cannot be excluded and the events are assessed as possibly related.