Multiple sclerosis pseudo relapse; COVID-19; unilateral lower extremity weakness following the second dose of mRNA-1273; 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. The occurrence of additional non-serious events is detailed below.   LITERATURE REFERENCE:     Concurrent medical conditions included Multiple sclerosis. Concomitant products included OCRELIZUMAB for Multiple sclerosis.   On an unknown date, the patient received second dose of mRNA-1273 (Spikevax) (unknown route) 1 dosage form. On an unknown date, received first 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) and MUSCULAR WEAKNESS (unilateral lower extremity weakness following the second dose of mRNA-1273). an unknown date, the patient experienced COVID-19 (COVID-19). At the time of the report, MULTIPLE SCLEROSIS PSEUDO RELAPSE (Multiple sclerosis pseudo relapse) and MUSCULAR WEAKNESS (unilateral lower extremity weakness following the second dose of mRNA-1273) had resolved and COVID-19 (COVID-19) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, SARS-CoV-2 test: (Positive) Patient tested positive for COVID-19 one day after the first dose of mRNA-1273.     For mRNA-1273 (Spikevax) (Unknown), the reporter did not provide any causality assessments.   This case belonged to patient number 9 of 9 patients reported. Treatment medications were not reported. Author retrospectively identified 250 Multiple sclerosis (MS) patients at institution who had received the initial vaccination cycle of the currently approved COVID-19 vaccines in the US. 151 of these patients also received a booster dose. side effects (SE) attributed to the COVID-19 vaccinations during a 90- day post-vaccination observation period were collected as part of the standard clinical care.88 Multiple sclerosis (MS) patients received the first and second doses of the mRNA-1273 vaccine. There were 2 cases of pseudo-relapse after the first mRNA-1273 dose and 4 cases following the second mRNA-1273 dose.  Most patients reporting a pseudo-relapse returned to baseline within less than 96 hours except for 2 cases that lasted for 1-2 weeks. There was no permanent neurological disability or severe, life-threatening adverse events reported. No treatment was recommended or performed during any of our pseudo-relapse cases. No acute cases of MS relapse were noted in our studied population that could be confirmed by clinical or radiological findings. Lower extremity weakness following the second dose spontaneously resolved within 96 h. There was a possibility that the patient contracted COVID-19 after their first dose due to the possible decreased immune-response for patients on B-cell therapy. Author concluded that COVID-19 vaccination was safe in patients with MS with a comparable side effects (SE) spectrum to the general population. The risk for clinical relapses were absent in cohort. Cases of temporary worsening of MS symptoms following SARS-CoV-2 were rare. These findings supported those reported by other recent studies and the CDC recommendation for MS patients to receive the FDA-approved COVID-19 prior to first dose administration. In general, authors did not identify a clear correlation between a type of disease modifying therapy (DMT) and incidence of SE   Company comment: This literature case concerns a patient of unknown age with no medical history information reported, who experienced the unexpected serious (medically significant) event of Multiple sclerosis pseudo relapse and non serious events of muscular weakness and COVID 19. The event of COVID 19 occurred one after the first dose of mRNA-1273, while Multiple sclerosis pseudo relapse and unilateral lower extremity weakness occurred following the second dose and spontaneously resolved within 96 h. As reported, there was a possibility that the patient contracted COVID-19 after their first dose due to the possible decreased immune-response for patients on B-cell therapy but pre-existent asymptomatic disease was also considered. No further information about the events was provided. The benefit-risk relationship of mRNA-1273 is not affected by this report.   This case was linked to US-MODERNATX, INC.-MOD-2023-732774 (E2B Linked Report).   Most recent FOLLOW-UP information incorporated above includes: On 16-Jul-2023: Follow-up received by safety on 18-Jul-2023 has an email with abstract and contains no new information. On 19-Jul-2023: Follow-up received by safety on 20-Jul-2023 has an email with full text article and contains no new information.; Sender's Comments:  US-MODERNATX, INC.-MOD-2023-732774:Master case ( MOD-2023-732774)