pseudo-tumorous edema in both shoulders/shoulder masses/COVID-19 vaccine prompting the growth of an injection site pseudo-tumor; Type IV hypersensitivity reaction; Shoulder soreness; Improper vaccination administration technique may have contributed to pseudo-tumorous edema in both shoulders; This literature-non-study case was reported in a literature article and describes the occurrence of VACCINATION SITE MASS (pseudo-tumorous edema in both shoulders/shoulder masses/COVID-19 vaccine prompting the growth of an injection site pseudo-tumor) and TYPE IV HYPERSENSITIVITY REACTION (Type IV hypersensitivity reaction) in a 53-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 prophylaxis. The occurrence of additional non-serious events is detailed below.       No Medical History information was reported.   On an unknown date, the patient received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On an unknown date, received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On an unknown date, the patient experienced VACCINATION SITE MASS (pseudo-tumorous edema in both shoulders/shoulder masses/COVID-19 vaccine prompting the growth of an injection site pseudo-tumor) (seriousness criterion medically significant), TYPE IV HYPERSENSITIVITY REACTION (Type IV hypersensitivity reaction) (seriousness criterion medically significant), ARTHRALGIA (Shoulder soreness) and WRONG TECHNIQUE IN PRODUCT USAGE PROCESS (Improper vaccination administration technique may have contributed to pseudo-tumorous edema in both shoulders). The patient was treated with PARACETAMOL (TYLENOL) at an unspecified dose and frequency. At the time of the report, VACCINATION SITE MASS (pseudo-tumorous edema in both shoulders/shoulder masses/COVID-19 vaccine prompting the growth of an injection site pseudo-tumor) and TYPE IV HYPERSENSITIVITY REACTION (Type IV hypersensitivity reaction) had resolved and ARTHRALGIA (Shoulder soreness) and WRONG TECHNIQUE IN PRODUCT USAGE PROCESS (Improper vaccination administration technique may have contributed to pseudo-tumorous edema in both shoulders) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Basophil count (0-0.2): 0.1 unit 10 and 0.9 %. On an unknown date, C-reactive protein increased (3-10 milligram per litre): 13.7 milligram per litre. On an unknown date, Eosinophil count (0-0.5): 0.1 unit 10 and 2.2 %. On an unknown date, Haematocrit (36-47 %): 38.3 %. On an unknown date, Haemoglobin (12-15.5 g/dL): 12.3 g/dL. On an unknown date, Immunoglobulins (0.0-3.0 %): 0.3 %. On an unknown date, Lymphocyte count (24-44 %): 16.3 % and 1.0 unit 10. On an unknown date, Magnetic resonance imaging: Showed localized pseudo-tumorous edema in both shoulders, one subcutaneous and the other intramuscular., 8 months after vaccine administration in right shoulder. Axial T2 and Coronal T2 images showed ill-defined fluid signal surrounding interspersed areas of fat. The involved area extended from surgical neck of the humerus to distal diaphysis, measuring approximately 14.9x8.2x1.8 cm., 10 months after vaccine administration in the left shoulder. Axial T1 weighted image showed predominately intramuscular edema within the lateral deltoid muscle measuring 5.6 cm anterior-posterior and 1.0 cm medial-lateral. Coronal T1 weighted image showed intramuscular edema within the lateral deltoid muscle measuring 10 cm proximal-distal. Axial T2 STIR and coronal T1 weighted images showed a slightly enlarged left axillary node (9.9x11.2x12.8 mm). and MRI to rule out malignancy on the more swollen side. The imaging showed abnormal regions within the subcutaneous tissue at the sites of the mass. Subcutaneous edematous tissue extended from the level of the humeral surgical neck to the distal diaphysis. On an unknown date, Mean cell haemoglobin (27.0-33 pg): 29.0 pg. On an unknown date, Mean cell haemoglobin concentration (32-36.5 g/dL): 32.1 g/dL. On an unknown date, Mean cell volume (80-96 fL): 90.3 fL. On an unknown date, Monocyte count (0-0.8): 0.7 unit 10 and 10.6 %. On an unknown date, Neutrophil count (1.5-8.5): 4.5 unit 10 and 69.7 %. On an unknown date, Nucleated red cells (0.40-0 %): 0 %. On an unknown date, Physical examination: normal range of motion with no tenderness to palpation. and deltoid strength 5/5 bilaterally, full active range of motion without discomfort or crepitus, no visual deformities (swelling, effusion, erythema) in the distal upper extremities and no joint tenderness on palpation.. On an unknown date, Platelet count (150-450): 320 unit 10. On an unknown date, Red blood cell count (4.00-5.40): 4.24 unit 10. On an unknown date, Red blood cell sedimentation rate abnormal (0-30 mm/hr): 21 mm/hr. On an unknown date, Red cell distribution width increased (11.5-14.5 %): 13.2 %.     For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter considered VACCINATION SITE MASS (pseudo-tumorous edema in both shoulders/shoulder masses/COVID-19 vaccine prompting the growth of an injection site pseudo-tumor), TYPE IV HYPERSENSITIVITY REACTION (Type IV hypersensitivity reaction), ARTHRALGIA (Shoulder soreness) and WRONG TECHNIQUE IN PRODUCT USAGE PROCESS (Improper vaccination administration technique may have contributed to pseudo-tumorous edema in both shoulders) to be related.    Concomitant medications were not provided.  The patient did not have a history of underlying medical, oncologic, orthopedic, or rheumatologic conditions, and there were no prior known soft-tissue masses. She had no history of drug allergy or allergic comorbidities. Also, there were no constitutional symptoms or adenopathy.  The depth of vaccine injections has a strong impact on tissue reaction. Deep IM injections are typically associated with fewer symptoms compared to SC or intradermal injections, possibly due to lower levels of nociceptors in muscle spindles compared with subcutaneous tissue and skin. This likely accounts for the lower amount of swelling and pain on the patient's left shoulder, where the imaging showed the reaction to be intramuscular, in contrast to the more symptomatic right shoulder subcutaneous reaction. The pain was described as a persistent discomfort which limited activities of daily living including driving, cooking, and work. These areas of localized swelling failed to resolve, despite treatment with heating pads and ice packs.  The subcutaneous edema found in the MRI of right shoulder lead us to believe that the needle length used, or the angle of administration, resulted in the needle tip not reaching the intramuscular tissue plane.  The patient's symptoms had fully resolved when she returned after 2 months (1 year after completing the injections).  Company Comment: This is a literature non-study case concerning a 53 year-old, female patient with no reported medical history (did not have a history of underlying medical, oncologic, orthopedic, or rheumatologic conditions, and there were no prior known soft-tissue masses), who experienced the serious (due to medically significant) unexpected, events of vaccination site mass and Type IV hypersensitivity reaction, which occurred 2 months after the second dose of mRNA-1273 vaccine. It was reported that 2 months after the second vaccination, patient developed bilateral injection-site pain, urticaria, decreased active range of motion, induration, and tenderness. The left shoulder (second dose administered) had a less florid reaction than the right (first dose administered). The pain was described as a persistent discomfort which limited activities of daily living including driving, cooking, and work. The patient took Intermittent paracetamol for the pain and initiated a home exercise program. Her general practitioner referred her to orthopedics. She waited another 3 months before consulting orthopedics. By this time, her pain ceased but the bilateral swelling persisted. Her initial treating orthopedic surgeon ordered a right shoulder magnetic resonance imaging (MRI) to rule out malignancy on the more swollen side. The imaging showed abnormal regions within the subcutaneous tissue at the sites of the mass. Subcutaneous edematous tissue extended from the level of the humeral surgical neck to the distal diaphysis. Blood tests showed mild Neutrophil and Monocyte increase and mild lymphocyte decrease (seven months after the second injection). Three months after visiting the initial orthopedist, the patient attended a different orthopedic clinic. At this visit, (10 months since receiving her injections) and the clinical examination showed normal range of motion with no tenderness to palpation. There were no rashes on inspection; however, edema and nodules to palpation were found in the lateral deltoid heads. Due to the persistent, left shoulder swelling, an MRI was performed, which showed similar findings of edema but in an intramuscular rather than subcutaneous location and the presence of a slightly enlarged axillary node. Additionally, Wrong technique in product usage process was reported in the case. In this case, the authors hypothesized that the patient experienced a florid type IV hypersensitivity reaction leading to a granulomatous response in a nodular and edematous fashion. The outcome was reported as recovered, 1 year after vaccination. No further clinical information was available for medical review. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.   Most recent FOLLOW-UP information incorporated above includes: On 04-May-2023: Live follow-up received on 04-May-2023 contains significant information: author details, citation details an patient information updated.; Sender's Comments: Company Comment: This is a literature non-study case concerning a 53 year-old, female patient with no reported medical history (did not have a history of underlying medical, oncologic, orthopedic, or rheumatologic conditions, and there were no prior known soft-tissue masses), who experienced the serious (due to medically significant) unexpected, events of vaccination site mass and Type IV hypersensitivity reaction, which occurred 2 months after the second dose of mRNA-1273 vaccine. It was reported that 2 months after the second vaccination, patient developed bilateral injection-site pain, urticaria, decreased active range of motion, induration, and tenderness. The left shoulder (second dose administered) had a less florid reaction than the right (first dose administered). The pain was described as a persistent discomfort which limited activities of daily living including driving, cooking, and work. The patient took Intermittent paracetamol for the pain and initiated a home exercise program. Her general practitioner referred her to orthopedics. She waited another 3 months before consulting orthopedics. By this time, her pain ceased but the bilateral swelling persisted. Her initial treating orthopedic surgeon ordered a right shoulder magnetic resonance imaging (MRI) to rule out malignancy on the more swollen side. The imaging showed abnormal regions within the subcutaneous tissue at the sites of the mass. Subcutaneous edematous tissue extended from the level of the humeral surgical neck to the distal diaphysis. Blood tests showed mild Neutrophil and Monocyte increase and mild lymphocyte decrease (seven months after the second injection). Three months after visiting the initial orthopedist, the patient attended a different orthopedic clinic. At this visit, (10 months since receiving her injections) and the clinical examination showed normal range of motion with no tenderness to palpation. There were no rashes on inspection; however, edema and nodules to palpation were found in the lateral deltoid heads. Due to the persistent, left shoulder swelling, an MRI was performed, which showed similar findings of edema but in an intramuscular rather than subcutaneous location and the presence of a slightly enlarged axillary node. Additionally, Wrong technique in product usage process was reported in the case. In this case, the authors hypothesized that the patient experienced a florid type IV hypersensitivity reaction leading to a granulomatous response in a nodular and edematous fashion. The outcome was reported as recovered, 1 year after vaccination. No further clinical information was available for medical review. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.