Seizures; This literature-non-study case was reported in a literature article and describes the occurrence of SEIZURE (Seizures) in a  patient of an unknown age and gender who received mRNA-1273 (Spikevax) for COVID-19 prophylaxis.        No Medical History information was reported.    On an unknown date, the patient received first dose of mRNA-1273 (Spikevax) (unknown route) 1 dosage form. On an unknown date, the patient experienced SEIZURE (Seizures) (seriousness criterion medically significant). At the time of the report, SEIZURE (Seizures) outcome was unknown.        The action taken with mRNA-1273 (Spikevax) (Unknown) was unknown.   For mRNA-1273 (Spikevax) (Unknown), the reporter did not provide any causality assessments.   Concomitant and treatment medications were not reported.  This case refers to a patient of unknown age and gender who experienced the seizure first dose of mRNA-1273 vaccine.   This study described simultaneous vaccination (SV) with primary series COVID-19 vaccines and assess 23 pre-specified health outcomes following SV among persons aged greater than or equal to 5 years in the Vaccine Safety Datalink (VSD). from December 11, 2020-May 21, 2022. Analyses assessed frequency of SV.   Rate ratios (RRs) were estimated by Poisson regression when the number of outcomes was greater than or equal to 5 across both doses, comparing outcome rates between COVID-19 vaccinees receiving SV and COVID-19 vaccinees receiving no SV in the 1-21 days following COVID-19 vaccine dose 1 and 1-42 days following dose 2 by SV type received.  The most frequent simultaneous vaccines were influenza, HPV, Tdap, and meningococcal. Outcomes following SV with COVID-19 vaccines were rare (total of 56 outcomes observed after dose 1 and dose 2. Overall rate of outcomes among COVID-19 vaccinees who received SV was not statistically significantly different than the rate among those who did not receive SV.  The most frequent simultaneous vaccines were influenza, HPV, Tdap, and meningococcal. Outcomes following SV with COVID-19 vaccines were rare (total of 56 outcomes observed after dose 1 and dose 2). Overall rate of outcomes among COVID-19 vaccines who received SV was not statistically significantly different than the rate among those who did not receive SV.  Company comment: This literature non-study case report concerns a patient of an unknown age and gender, with no medical history available at the time of the report, who experienced serious (medically significant) unexpected event of special interest - Seizure. The event occurred after the patient had received the first dose of the mRNA-1273 vaccine. The exact temporal relationship between vaccination and event occurrence cannot be determined, as the results were presented cumulatively, however, the authors stated that days to diagnosis ranged from 1 to 14 days post vaccination (median 13 days). The outcome of the event remained unknown and no additional details regarding clinical course of the event were available at this moment. It also remained unspecified what was simultaneous vaccination that the patient received when mRNA-1273 vaccine was administered. No further details were available for medical assessment. The authors stated that combined pre-specified health outcomes observed among persons who received simultaneous vaccination with COVID-19 vaccine were rare and not statistically significantly different compared to persons who did not receive simultaneous vaccination with COVID-19 vaccine. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.   This case was linked to US-MODERNATX, INC.-MOD-2023-731103 (Linked Report).   Most recent FOLLOW-UP information incorporated above includes: On 30-Jun-2023: Live follow-up received by safety on 30-Jun-2023, contains significant information: Reporter details, dose details and an updated narrative.; Sender's Comments: This literature non-study case report concerns a patient of an unknown age and gender, with no medical history available at the time of the report, who experienced serious (medically significant) unexpected event of special interest - Seizure. The event occurred after the patient had received the first dose of the mRNA-1273 vaccine. The exact temporal relationship between vaccination and event occurrence cannot be determined, as the results were presented cumulatively, however, the authors stated that days to diagnosis ranged from 1 to 14 days post vaccination (median 13 days). The outcome of the event remained unknown and no additional details regarding clinical course of the event were available at this moment. It also remained unspecified what was simultaneous vaccination that the patient received when mRNA-1273 vaccine was administered. No further details were available for medical assessment. The authors stated that combined pre-specified health outcomes observed among persons who received simultaneous vaccination with COVID-19 vaccine were rare and not statistically significantly different compared to persons who did not receive simultaneous vaccination with COVID-19 vaccine. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report. US-MODERNATX, INC.-MOD-2023-731103:appendicitis