couldn't move it /When I sit for too long, I have difficulty standing; discomfort when I lean on it; it hurts, pain in my arm; swelled; moderate fluid collecting in my calf; acute pain in his left knee; didn't feel well; fatigue; muscle spasms; warm to the touch; This spontaneous case was reported by a consumer (subsequently medically confirmed) and describes the occurrence of MUSCLE SPASMS (muscle spasms), JOINT SWELLING (swelled), FLUID RETENTION (moderate fluid collecting in my calf), MALAISE (didn't feel well) and MOBILITY DECREASED (couldn't move it /When I sit for too long, I have difficulty standing) in a 49-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     Concomitant products included SIMVASTATIN, TRIAMCINOLONE ACETONIDE (NASACORT), OMEPRAZOLE MAGNESIUM (PRILOSEC [OMEPRAZOLE MAGNESIUM]) and FINASTERIDE for an unknown indication.   On 19-Jan-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 16-Feb-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to 1 dosage form. On 19-Jan-2021, the patient experienced MUSCLE SPASMS (muscle spasms) and FEELING HOT (warm to the touch). On 20-Jan-2021, the patient experienced MALAISE (didn't feel well) and FATIGUE (fatigue). On an unknown date, the patient experienced JOINT SWELLING (swelled), FLUID RETENTION (moderate fluid collecting in my calf), MOBILITY DECREASED (couldn't move it /When I sit for too long, I have difficulty standing), MUSCULOSKELETAL DISCOMFORT (discomfort when I lean on it), PAIN IN EXTREMITY (it hurts, pain in my arm) and ARTHRALGIA (acute pain in his left knee). The patient was treated with CELECOXIB (CELEBREX) for Adverse event, at a dose of UNK dosage form; DOXYCYCLINE for Adverse event, at a dose of UNK dosage form; HYDROCODONE for Adverse event, at a dose of UNK dosage form and PARACETAMOL (TYLENOL) for Adverse event, at a dose of UNK dosage form. On 19-Jan-2021, MUSCLE SPASMS (muscle spasms) had resolved. On 22-Jan-2021, MALAISE (didn't feel well), FEELING HOT (warm to the touch) and FATIGUE (fatigue) had resolved. At the time of the report, JOINT SWELLING (swelled), MOBILITY DECREASED (couldn't move it /When I sit for too long, I have difficulty standing), MUSCULOSKELETAL DISCOMFORT (discomfort when I lean on it), PAIN IN EXTREMITY (it hurts, pain in my arm) and ARTHRALGIA (acute pain in his left knee) outcome was unknown and FLUID RETENTION (moderate fluid collecting in my calf) was resolving.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Full blood count: normal (normal) Full Blood panel test results were normal.. On an unknown date, Lyme disease: negative (Negative) The patient had moderate fluid collecting in his calf but tested negative to Lyme's disease.. On an unknown date, Magnetic resonance imaging: mild to moderate inflammation (Inconclusive) MRI of leg showed no underlying trauma, but mild to moderate inflammation..     For mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular), the reporter did not provide any causality assessments.   No concomitant medications reported. Reported that his inflammation markers were low and a rheumatoid arthritis panel was negative. Also reported that he still has discomfort when he leans on it and it hurts when he sits for too long.    Most recent FOLLOW-UP information incorporated above includes: On 18-May-2021: Initial Addition-1 On 18-May-2021: Email mentions wrong person contacted. On 21-May-2021: NNI