Acute myocarditis; This literature-study case was reported in a literature article and describes the occurrence of MYOCARDITIS (Acute myocarditis) in an adult male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination.   No Medical History information was reported.    On an unknown date, the patient received dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On an unknown date, the patient experienced MYOCARDITIS (Acute myocarditis) (seriousness criteria hospitalization prolonged and medically significant). At the time of the report, MYOCARDITIS (Acute myocarditis) had resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, SARS-CoV-2 test: negative (Negative) All were hospitalized and tested negative for SARS-CoV-2 by polymerase chain reaction on admission..     The action taken with mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown) was unknown.   For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter did not provide any causality assessments.   No relevant concomitant medications were reported.   No treatment information was provided.  They calculated incidence rates and 95% confidence intervals (CIs) of myocarditis using vaccine administration as the denominator and compared it with the incidence of myocarditis in unexposed individuals between 14-Dec-202 and 20-Jul-2020; and with vaccinated individuals during a 10 day period 1 year prior to vaccination.  There were 15 cases of confirmed myocarditis in the vaccinated group (2 after the first dose and 13 after the second).  Of the patients with myocarditis post vaccination, no one had prior cardiac disease.  Fourteen (93%) reported chest pain between 1 to 5 days after vaccination. Symptoms resolved with conservative management in all cases; no patients required intensive care unit admission or readmission after discharge.  Author concluded that In this population-based cohort study of 2,392,924 individuals who received at least 1 dose ofCOVID-19mRNAvaccines, acute myocarditis was rare, at an incidence of 5.8 cases per 1 million individuals after the second dose (1 case per 172,414 fully vaccinated individuals). The signal of increased myocarditis in young men warrants further investigation.  This vaccinated cohort is unique in its racial and ethnic diversity and in receiving care at community hospitals with treatment reflective of real-world practice. Limitations of this study include the observational design; short follow-up time; absence of myocardial biopsy for definitive diagnosis; lack of uniform testing of all cases; possible more extensive workup of chest pain in vaccinated individuals during the immediate post-vaccination period; and possible under-diagnosis of subclinical cases. No relationship between COVID-19 mRNA vaccination and post-vaccination myocarditis can been established given the observational nature of this study.   This case was linked to MOD-2021-350207, MOD-2021-353153, MOD-2021-353154, MOD-2021-353156, MOD-2021-353157, MOD-2021-353158 (Patient Link).   Most recent FOLLOW-UP information incorporated above includes: On 13-Oct-2021: Follow up received by safety on 13-Oct-2021 has Email with a regulatory authority and does not contain any new information.; Sender's Comments: This case concerns an adult male patient with no relevant medical history, who experienced the expected event of myocarditis, which required hospitalization. The event occurred on an unknown date after the dose of Moderna COVID-19 Vaccine. Symptoms resolved with conservative management and did not require intensive care unit admission or readmission after discharge. Myocardial biopsy for definitive diagnosis was not performed. The rechallenge was not applicable as no information regarding dose number was provided. The benefit-risk relationship of Moderna COVID-19 Vaccine is not affected by this report.