Myocarditis; This literature-non-study case was reported in a literature article and describes the occurrence of MYOCARDITIS (Myocarditis) 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 second dose of mRNA-1273 (Spikevax) (unknown route) 1 dosage form. On an unknown date, the patient experienced MYOCARDITIS (Myocarditis) (seriousness criterion medically significant). At the time of the report, MYOCARDITIS (Myocarditis) had resolved.        For mRNA-1273 (Spikevax) (Unknown), the reporter considered MYOCARDITIS (Myocarditis) to be related.    This case referred to a patient who presented with pericarditis following Spikevax.  Concomitant medications were not reported.  From 14 December 2020 to 9 October 2022, 2 184 449 first and 2 036 948 second doses of mRNA-1273 (Moderna) were administered. 156160 mRNA-1273 booster doses were administered. Eighty-eight percent of vaccine recipients were men. Among vaccinees, more than 65% were White and 18% were Black (20% Black among recipients of booster doses). Over 60% of vaccinees were greater than equal to 65 years old. About 9% of those who received primary doses were between 18 and 39 years old. Those aged 1839 were less likely to receive booster doses as compared with the primary doses.  178 potential cases of myocarditis/pericarditis within the 21-day risk window among vaccinees of any age and 22 potential cases among those aged 18-39 years. The observed-to-expected ratio for myocarditis/pericarditis among vaccine recipients of all ages ranged from 0.7 to 1.3 for Moderna. 33 cases of myocarditis/pericarditis were confirmed among vaccine recipients of any age. This corresponds with overall incidence rates ranging from 0.46 per million doses administered for Moderna dose 1. The incidence rate among first booster doses was 4.32 for Moderna. Overall, 31 of 33 (94%) were male. Confirmed cases had a median age of 62 years. The median time to symptom onset was 3 days after vaccine administration. Out of 33, 4 (12%) had a history of COVID-19 infection. Among the adjudicated diagnoses (ie, pericarditis or myocarditis/myopericarditis), pericarditis was the most common overall at 20 of 33 (61%). Among the younger group (18-39 years), 1 received Moderna.  The patients were treated with colchicine and nonsteroidal anti-inflammatory drug.   This case was linked to US-MODERNATX, INC.-MOD-2023-734758 (Linked Report).  Company Comment: This is a Literature-Non-Study case concerning an adult patient of unknown age and gender, with no reported medical history, who experienced the unexpected serious (medically significant) event of myocarditis within the 21-day after the administration of the second dose of mRNA-1273 vaccine. The event was clinically resolved before day 120. No further information on clinical course, investigations done and treatment received for this specific patient was available in the report. The benefit-risk relationship of mRNA-1273 Vaccine is not affected by this report.   Most recent FOLLOW-UP information incorporated above includes: On 27-Jul-2023: Live follow-up received by safety on 27-JUL-2023 has email with full text article that contains significant information: Reporter information, literature information, dose information and iNarrative updated.; Sender's Comments: This is a Literature-Non-Study case concerning an adult patient of unknown age and gender, with no reported medical history, who experienced the unexpected serious (medically significant) event of myocarditis within the 21-day after the administration of the second dose of mRNA-1273 vaccine. The event was clinically resolved before day 120. No further information on clinical course, investigations done and treatment received for this specific patient was available in the report. The benefit-risk relationship of mRNA-1273 Vaccine is not affected by this report. US-MODERNATX, INC.-MOD-2023-734758:Same literature (Master case)