MS exacerbation; ataxia/dysmetria; Dysmetria in right upper extremity; This literature-study case was reported in a literature article and describes the occurrence of MULTIPLE SCLEROSIS (MS exacerbation) in a 35-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.        The patient's past medical history included Clinically isolated syndrome (Patient diagnosed with clinically isolated demyelinating syndrome (CIS) 11 years ago after she developed a left optic neuritis and brain MRI lesions) and Optic neuritis. Previously administered products included for Product used for unknown indication: INTERFERON BETA-1A (Patient was placed on weekly intramuscular interferon beta-1a.Despite starting disease-modifying therapy, she developed new brain lesions 10 months later and and she was diagnosed as converted to relapsingremitting). Past adverse reactions to the above products included No adverse event with INTERFERON BETA-1A. Concurrent medical conditions included Relapsing-remitting multiple sclerosis and Myelitis (developed a symptomatic partial myelitis associated with an acute enhancing MRI lesion in the cervical spinal cord). Concomitant products included NATALIZUMAB for Multiple sclerosis.   On 05-Jan-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. In 2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On an unknown date, the patient experienced MULTIPLE SCLEROSIS (MS exacerbation) (seriousness criterion medically significant), ATAXIA (ataxia/dysmetria) and DYSMETRIA (Dysmetria in right upper extremity). The patient was treated with METHYLPREDNISOLONE (intravenous) for Neurologic symptoms, at a dose of 1000 mg once a day. At the time of the report, MULTIPLE SCLEROSIS (MS exacerbation), ATAXIA (ataxia/dysmetria) and DYSMETRIA (Dysmetria in right upper extremity) had resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Disability assessment scale: 1.0 Expanded Disability Status Scale (EDSS) score of 1.0 with no evidence of clinical or MRI disease activity over the next 7 years., 1.0 EDSS score back to the 1.0 baseline and 2.5 (abnormal) EDSS score of 2.5.. On an unknown date, JC polyomavirus test negative: negitive (Negative) Serum JC virus test negitive. On an unknown date, Magnetic resonance imaging: abnormal (abnormal) Brain lesions, abnormal (abnormal) MRI showed a newT2 hyperintense lesion in the right cerebellum that enhanced with gadolinium., abnormal (abnormal) acute enhancing MRI lesion in the cervical spinal cord and normal (normal) Follow up MRI, 30 days after symptom onset, showed nearly complete resolution of the cerebellar lesion gadolinium enhancement. On an unknown date, Neutralising antibodies negative: negitive (Negative) natalizumab neutralizing antibodies.     For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter considered MULTIPLE SCLEROSIS (MS exacerbation), ATAXIA (ataxia/dysmetria) and DYSMETRIA (Dysmetria in right upper extremity) to be possibly related.    Axial (a) and sagittal (e) T2 FLAIR MRI obtained 18 months prior to onset of new neurologic symptoms show two typical MS lesions in the corpus callosum, but no lesions in the cerebellum. Axial (b) and sagittal (f) T2 FLAIR and T1 post-gadolinium axial (c) and sagittal (g) MRI after COVID-19 vaccination and new neurologic symptom onset showing a new 1.5 × 1.4 × 1.9 cm T2 hyperintense lesion in the cerebellum with open-ring enhancement. Axial T1 post-contrast MRI (d) obtained30 days after symptom onset, and after high dose intravenous methylprednisolone, shows nearly complete resolution of the gadolinium enhancement of the lesion. Her other MS lesions remained stable: sagittal STIR (h) and axial T2 (i) of the cervical spinal cord show a T2 hyperintense demyelinating lesion. T2 FLAIR of the brain (jo) show numerous typical MS lesions including one in the right cerebellum Prior to the vaccination patient had symptomatic partial myelitis associated with an acute enhancing MRI lesion. Her symptoms resolved after 3 days of high dose (1000 mg daily) intravenous methylprednisolone (IVMP).  The disease modifying therapy was switched to natalizumab which led to a long period of disease stability at an Expanded Disability Status Scale (EDSS) score of 1.0 with no evidence of clinical or MRI disease activity over the next 7 years. After receiving second dose of vaccine  28 days post the first dose, patient had mild systemic side effects lasting only for 1 day. Patient received 2 days of 1000 mg IVMP per day based on the assumption that this was an MS relapse. It was reported that all new neurologic symptoms had fully resolved.  Company Comment: This case refers to a 35-year-old female patient with a medical history of Relapsing-remitting multiple Sclerosis and Myelitis who experienced the unexpected events of Multiple sclerosis, Ataxia and Dysmetria on an unknown date. The reporter has assessed the events as possibly to causality assessment was provided by the report   This case was linked to MOD-2021-318473, MOD-2021-318474.   Most recent FOLLOW-UP information incorporated above includes: On 14-Sep-2021: Follow up received by safety on 15-Sep-2021 included an Email with FTA received from Team and does not contain any new information.; Sender's Comments: This case refers to a 35-year-old female patient with a medical history of Relapsing-remitting multiple Sclerosis and Myelitis who experienced the unexpected events of Multiple sclerosis, Ataxia and Dysmetria on an unknown date. The reporter has assessed the events as possibly to causality assessment was provided by the reporter. The benefit-risk relationship of Spikevax is not affected by this report.