Multiple sclerosis pseudo-relapse; This literature-non-study case was reported in a literature article and describes the occurrence of MULTIPLE SCLEROSIS PSEUDO RELAPSE (Multiple sclerosis pseudo-relapse) in a  patient of an unknown age and gender who received mRNA-1273 (Spikevax) for COVID-19 prophylaxis.   Concurrent medical conditions included Multiple sclerosis.   On an unknown date, the patient received first dose of mRNA-1273 (Spikevax) (unknown route) 1 dosage form. On an unknown date, received second dose of mRNA-1273 (Spikevax) (unknown route) dosage was changed to 1 dosage form. On an unknown date, the patient experienced MULTIPLE SCLEROSIS PSEUDO RELAPSE (Multiple sclerosis pseudo-relapse) (seriousness criterion medically significant). At the time of the report, MULTIPLE SCLEROSIS PSEUDO RELAPSE (Multiple sclerosis pseudo-relapse) had resolved.        For mRNA-1273 (Spikevax) (Unknown), the reporter did not provide any causality assessments.   This case belonged to patient number 2 of 8 patients reported. Concomitant medication was not specified, however, patients included in the study were administered with B-Cell Therapies (ocrelizumab and rituximab), Alemtuzumab, S1P-modulators (fingolimod and ozanimod), Teriflunomide, Fumarates (dimethyl fumarate and diroximel fumarate), Natalizumab, Glatiramer acetate and Interferons Cladribine No treatment medication was reported. Patient did not experience lymphadenopathy and arthralgia. Symptoms mainly consisted of weakness and severe fatigue. Author stated that, of note, most patients reporting a pseudo-relapse returned to baseline within less than 96 h except for the 2 cases. There was no permanent neurological disability or severe, life-threatening adverse events reported. No treatment was recommended or performed during any of these pseudo-relapse cases. No acute cases of MS relapse were noted in our studied population that could be confirmed by clinical or radiological findings. The reported pseudo-relapses largely consisted of a transient resurgence of MS symptoms, including paresthesia, lower extremity weakness, dysarthria, and cognitive impairment. Author also stated that altogether, the risk of having a pseudo-relapse after receiving BNT162b2 and mRNA-1273 was low. It cannot be determined if the mRNA vaccine variants directly caused a pseudo-relapse in this MS population. Side effects from the vaccine such as fever or myalgia could temporarily provoke old symptoms similar to a systemic infection. Most cases of pseudo-relapses resolved completely within 96 h except for 2 cases that lasted for 1-2 weeks.   This case was linked to US-MODERNATX, INC.-MOD-2023-732774 (Linked Report).  Company comment: This is a literature non-study case concerning a patient of an unknown age (mean age 55.3) and gender with past medical history of Multiple sclerosis, who experienced the serious unexpected medically significant event multiple sclerosis pseudo relapse. The event occurred after receiving a dose of mRNA-1273 vaccine (event and vaccine date and dose were not provided). The patient received 2 doses of the mRNA-1273 vaccine. No treatment or concomitant medication was provided. The event was reported as resolved. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.   Most recent FOLLOW-UP information incorporated above includes: On 11-Jul-2023: Follow up received by safety on 12-Jul-2023 contains significant information: Reporter information, citation details, current condition, suspect details and event details were updated.; Sender's Comments: Company comment: This is a literature non-study case concerning a patient of an unknown age (mean age 55.3) and gender with past medical history of Multiple sclerosis, who experienced the serious unexpected medically significant event multiple sclerosis pseudo relapse. The event occurred after receiving a dose of mRNA-1273 vaccine (event and vaccine date and dose were not provided). The patient received 2 doses of the mRNA-1273 vaccine. No treatment or concomitant medication was provided. The event was reported as resolved. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report. US-MODERNATX, INC.-MOD-2023-732774: