COVID-19 vaccination has been available since December 2020. On 10 May, 2021, the Food and Drug Administration approved the use of the BNT162b2 vaccine in the paediatric population aged 12 years and older. Vaccination of youth with an mRNA vaccine against SARS-CoV-2 has been recommended by the American Academy of Pediatrics and Centers for Disease Control and Prevention. ^{1,Reference Wallace, Woodworth and Gargano2} A single case of myocarditis in an adult following administration of the BNT162b2 vaccine has been reported from Spain. ^{Reference García, Ortega and Fernández3} Recently, there have been several reports about myocarditis following mRNA vaccines against SARS-CoV-2. ⁴ We describe, for the first time, adolescents presenting with chest pain and imaging evidence of myocarditis in close temporal association with the BNT162b2 vaccination.

Two adolescent males, aged 15–16 years of age, presented in the Emergency Department with chest pain within 3 days of BNT162b2 vaccine administration, one of them after the first, the other after the second dose of the vaccine. One patient noted mild and typical vaccine-related symptoms including tactile fever, headache, and tender vaccination site within a day of vaccine administration, while the other patient had no such symptoms. Within a couple of days after vaccination, both patients developed acute onset, mid-sternal, non-radiating chest pain associated with chest tightness. One patient had a history of mild intermittent asthma, otherwise, they had no known medical conditions and no prior surgeries.

Their initial vital signs were notable for sinus tachycardia with heart rate of 108–116 beats per minute, but normal blood pressure. They had a normal cardiac exam without a murmur or friction rub. Inflammatory markers were mildly elevated (Table 1). Complete blood count was notable for neutrophilia without leukocytosis. Cardiac enzymes were elevated in both cases at presentation (Table 1). Infectious workup including immunoglobulin G and real-time reverse transcription polymerase chain reaction for SARS-CoV-2 and respiratory viral panel polymerase chain reaction containing the most common aetiologic agents of viral myocarditis were negative in both patients.

Table 1. Demographics, clinical findings, and diagnostic test results of the patients with myocarditis following BNT162b2 vaccine administration

CKMB = creatine kinase myocardial band; CRP = C-reactive protein; ESR = erythrocyte sedimentation rate; IgG = immunoglobulin G; LVEF = left ventricular ejection fraction; NT-proBNP = N-terminal prohormone of brain natriuretic peptide; PCR = respiratory viral panel polymerase chain reaction; Respiratory viral panel RT-PCR = real-time reverse transcription polymerase chain reaction; SpO2 = blood oxygen saturation.

Chest X-rays were unremarkable. Electrocardiograms showed ST elevation and T wave inversion in lateral leads (Fig 1). Both patients had normal left ventricular systolic function on echocardiogram (Table 1). Small areas of increased echogenicity could be detected throughout the myocardium in one of the patients, especially in the interventricular septum and lateral wall of the left ventricle (Fig 1). Cardiac MRI with early gadolinium enhancement using electrocardiogram-gated turbo spin echo T1-weighted sequences showed mild global early enhancement of the myocardium, with pronounced enhancement in the subendocardial layer of the left ventricle (Fig 1), findings consistent with inflammation of the myocardium without evidence of myocardial necrosis, fibrosis, or oedema. Cardiac catheterisation was not performed as there was low suspicion for acute coronary syndrome and the cardiac MRI was consistent with myocarditis.

Figure 1. Electrocardiogram, echocardiogram, and cardiac MRI findings associated with myocarditis after BNT162b2 vaccination. ( a ) Electrocardiogram shows ST segment elevation, especially in the lateral leads. ( b ) The echocardiogram shows patchy echogenic foci in the left ventricle with intact left ventricular systolic function. Arrow indicates echogenic areas in the interventricular septum. ( c ) Cardiac MRI with gadolinium enhancement using electrocardiogram-gated turbo spin echo T1-weighted sequences demonstrates early enhancement of the myocardium of the left ventricle, especially in the subendocardial layer, but no necrosis or significant oedema, consistent with myocarditis. Arrow indicates bright, enhanced areas of the left ventricular myocardium. Insert shows pre-gadolinium image with no myocardial enhancement.

One patient received intravenous immunoglobulin, while the other patient improved without any treatment. Echocardiograms continued to show normal left ventricular function throughout the hospitalisation. Troponin T peaked at 832 and 1210 ng/L, but creatine kinase myocardial band did not increase beyond initial levels (Table 1). Chest pain resolved a day after admission and both patients were discharged from the hospital within 4 days of admission. Electrocardiograms showed improved, but continued mild ST segment elevation at discharge.