Most confirmed cases of myocarditis after Covid-19 vaccination have occurred in males 16 years and older after receiving the second dose of mRNA COVID-19 vaccine. Symptoms typically appear within several days of vaccination. [1]

The Centers for Disease Control and Prevention (CDC) states, "cases of myocarditis and pericarditis in adolescents and young adults have been reported more often after getting the second dose than after the first dose of one of these two mRNA COVID-19 vaccines. These reports are rare and the known and potential benefits of COVID-19 vaccination outweigh the known and potential risks, including the possible risk of myocarditis or pericarditis." [2]

On June 23rd, 2021, the following statement was co-signed by the U.S. Department of Health and Human Services (HHS), Centers for Disease Control and Prevention (CDC), American Academy of Family Physicians (AAFP), American Academy of Pediatrics (AAP), American College of Obstetricians and Gynecologists (ACOG), American College of Physicians (ACP), American Heart Association, American Hospital Association (AHA), American Medical Association (AMA), American Nurses Association (ANA), American Public Health Association (APHA), Association of Public Health Laboratories, Association of State and Territorial Health Officials (ASTHO), Big Cities Health Coalition, Council of State and Territorial Epidemiologists, Infectious Diseases Society of America, and National Association of County and City Health Officials (NACCHO):

“The facts are clear: this is an extremely rare side effect, and only an exceedingly small number of people will experience it after vaccination. Importantly, for the young people who do [become infected], most cases are mild, and individuals recover often on their own or with minimal treatment. In addition, we know that myocarditis and pericarditis are much more common if you get COVID-19, and the risks to the heart from COVID-19 infection can be more severe.” [3]

According to the new update from the Advisory Committee on Immunization Practices (ACIP) published earlier July 9, 2021, the panel has noticed an elevated risk of myocarditis, particularly among males aged 12-29 years after receiving mRNA COVID-19 vaccines. After reviewing reported cases of myocarditis and pericarditis, on June 23, 2021, ACIP states the benefits of receiving mRNA COVID-19 vaccines apparently outweigh the risks in adolescents and young adults. Accordingly, the Emergency Use Authorization (EUA) also reflects the information on myocarditis for public awareness. [4]

Among patients <30 years with reported myocarditis during May 1 – June 11, 2021, 323 of the 484 cases were determined to meet CDC's criteria of myocarditis, pericarditis, or myopericarditis based on provider interview and chart-review of the medical records. The median age of these confirmed cases was 19 (range, 12−29), and 291 (90.1%) of them were male. From vaccination to symptom onset, the median interval was two days (range, 0-40 days), and 309 (96%) were hospitalized for further management. By the time of case review, 95% of the patients had been discharged after mainly receiving conservative treatment, such as nonsteroidal anti-inflammatory drugs. Continuous follow-up is warranted to investigate long-term effects of myocarditis after receiving COVID-19 vaccines. Utilizing VAERS data with onset within seven days after dose 2 of an mRNA vaccine administered to males 12-29 years old, myocarditis reporting rates were 40.6 cases per million. The reporting rate was 62.8 myocarditis cases per million-second doses of mRNA COVID-19 vaccine administered among adolescents aged 12−17. In conclusion, ACIP emphasized the benefits over risks in this particular patient population, and the need to monitor and disseminate the information among the public and providers. [4]

Per the vaccine adverse effects reporting system (VAERS) database on July 27th, 2021, there have been 351 reports of myocarditis in pediatric patients. The majority have been associated with Pfizer (n = 347). [5]

The rate of myocarditis after the vaccination is potentially lower than in children who become infected. A cross‐sectional study included all children ≤18 years diagnosed with microbiologically confirmed (PCR analysis on nasopharyngeal swab) COVID‐19 (through a nasopharyngeal swab from March 2020 to October 2020; N= 129; mean age of 11 ± 4.4 years, 62 (48.1%) female). During the acute COVID‐19, 33 children (25.6%) were asymptomatic, and 96 (74.4%) had symptoms. Overall, 6 (4.7%) children were hospitalized, and 3 (2.3%) needed pediatric intensive care unit admission. After the initial diagnosis of COVID‐19, three developed multisystem inflammatory syndrome (2.3%) and two myocarditis (1.6%). [6]