Experienced seizure episodes; Muscle weakness; Stiffness; Joint pain; Loss of motor skills, couldn't use hands, lost control of her arms, legs and muscle control; Experienced myoclonus; Her head went back and forth; Had a loss of speech / could not communicate but she could hear people talking during her episode; She went from 100% strength to 50% strength; This spontaneous case was reported by a consumer (subsequently medically confirmed) and describes the occurrence of SEIZURE (Experienced seizure episodes), MUSCULAR WEAKNESS (Muscle weakness), MUSCULOSKELETAL STIFFNESS (Stiffness), ARTHRALGIA (Joint pain), ATAXIA (Loss of motor skills, couldn't use hands, lost control of her arms, legs and muscle control), MYOCLONUS (Experienced myoclonus), POSTURE ABNORMAL (Her head went back and forth), DYSARTHRIA (Had a loss of speech / could not communicate but she could hear people talking during her episode) and ASTHENIA (She went from 100% strength to 50% strength) in a 47-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch no. 039B21A) for COVID-19 vaccination.     The patient's past medical history included COVID-19 (Patient tested positive but not hospitalized.) on 09-Dec-2020.    On 14-Apr-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 21-Apr-2021, the patient experienced SEIZURE (Experienced seizure episodes) (seriousness criteria hospitalization and medically significant), MUSCULAR WEAKNESS (Muscle weakness) (seriousness criterion hospitalization), MUSCULOSKELETAL STIFFNESS (Stiffness) (seriousness criterion hospitalization), ARTHRALGIA (Joint pain) (seriousness criterion hospitalization), ATAXIA (Loss of motor skills, couldn't use hands, lost control of her arms, legs and muscle control) (seriousness criterion hospitalization), MYOCLONUS (Experienced myoclonus) (seriousness criterion hospitalization), POSTURE ABNORMAL (Her head went back and forth) (seriousness criterion hospitalization), DYSARTHRIA (Had a loss of speech / could not communicate but she could hear people talking during her episode) (seriousness criterion hospitalization) and ASTHENIA (She went from 100% strength to 50% strength) (seriousness criterion hospitalization). The patient was hospitalized from 21-Apr-2021 to 23-Apr-2021 due to ARTHRALGIA, ASTHENIA, ATAXIA, DYSARTHRIA, MUSCULAR WEAKNESS, MUSCULOSKELETAL STIFFNESS, MYOCLONUS, POSTURE ABNORMAL and SEIZURE. The patient was treated with Physical therapy for Muscular weakness. At the time of the report, SEIZURE (Experienced seizure episodes), MUSCULAR WEAKNESS (Muscle weakness), MUSCULOSKELETAL STIFFNESS (Stiffness), ARTHRALGIA (Joint pain), ATAXIA (Loss of motor skills, couldn't use hands, lost control of her arms, legs and muscle control), MYOCLONUS (Experienced myoclonus), POSTURE ABNORMAL (Her head went back and forth), DYSARTHRIA (Had a loss of speech / could not communicate but she could hear people talking during her episode) and ASTHENIA (She went from 100% strength to 50% strength) outcome was unknown.        mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosing remained unchanged.       No concomitant medications were reported. Treatment information was not provided.  The reporter stated that the patient was not able to speak and it took time for her to speak again post the episodes. The physicians were not able to determine what was wrong with her at that time and received outpatient physical therapy treatment.  Company Comment: Based on the current available information and temporal association between the use of the product and the start date of the events, a causal relationship cannot be excluded. Further information has been requested.   This case was linked to MOD-2021-293196 (Patient Link).; Sender's Comments: Based on the current available information and temporal association between the use of the product and the start date of the events, a causal relationship cannot be excluded. Further information has been requested.