Cellulitis; the injection site became red; the injection site became swollen; the injection site became hot; it was itchy; hives at the injection site; The PA felt like a contaminated injection needle caused the reaction; Raised hives across the whole injection area; A spontaneous report was received from a 53-year-old female healthcare professional, who was also the patient, who received Moderna's COVID-19 vaccine (mRNA-1273) and experienced cellulitis, the injection site became red, the injection site became swollen, the injection site became hot, it was itchy, hives at the injection site, the PA felt like a contaminated injection needle caused the reaction, and raised hives across the whole injection area.   The patient's medical history was not provided.  No concomitant medications were reported.  On 23 Dec 2020, prior to the onset of the events, the patient received their first of two planned doses of mRNA-1273 (Lot number: 039K20A) intramuscularly in the left bicep for prophylaxis of COVID-19 infection.   On 24 Dec 2020, one day after vaccination, the injection site of the patient became swollen, red, and hot.    On 28 Dec 2020, the symptoms started to fade.    On 29 Dec 2020, the patient was itchy and experienced hives at the injection site.    On 31 Dec 2020, the patient went to urgent care with raised hives across the whole injection area.  The Physician's Assistant at the urgent care felt that it was cellulitis caused by a contaminated injection needle and treated the patient with cefalexin. Within 24 hours of treatment, the event resolved.    Action taken with mRNA-1273 in response to the events was not reported.   The outcome of the events cellulitis, the injection site became red, the injection site became swollen, the injection site became hot, it was itchy, hives at the injection site, the PA felt like a contaminated injection needle caused the reaction, and raised hives across the whole injection area was considered resolved on 01 Jan 2021.; Reporter's Comments: Company comment: This case concerns a 53-year-old female patient, who experienced a serious event of Cellulitis and non-serious events of Injection site erythema, Injection site swelling, Injection site warmth, Injection site pruritus, Injection site urticaria (onset date of 29DEC2020), Exposure via contaminated device, Injection site reaction, and Injection site urticaria (onset date of 31DEC2020). The events of Injection site erythema, Injection site swelling, and Injection site warmth occurred on the next day of administration of their first of two planned doses of mRNA-1273 (Lot number: 039K20A). The events of Injection site pruritus, Injection site urticaria (onset 29DEC2020), and Cellulitis occurred 6 days after mRNA-1273 administration. The event of Injection site urticaria (onset 31DEC2020) occurred 8 days after mRNA-1273 administration. Treatment with antibiotics was performed with positive therapeutic response. The events of Exposure via contaminated device and Injection site reaction were considered to occur on the same day of mRNA-1273 administration by the healthcare worker. Based on the current available information and temporal association between the use of the product and the start date of the events of Cellulitis, Injection site erythema, Injection site swelling, Injection site warmth, Injection site pruritus, Injection site urticaria (onset date of 29DEC2020), Injection site reaction, and Injection site urticaria (onset date of 31DEC2020), a causal relationship cannot be excluded.  Causality of the event of Exposure via contaminated device is assessed as Not applicable, because the event is a procedural issue.