Background: Understanding the clinical course and short-term outcomes of suspected myocarditis following COVID-19 vaccination has important public health implications in the decision to vaccinate youth. Methods: We retrospectively collected data on patients <21 years-old presenting before 7/4/2021 with suspected myocarditis within 30 days of COVID-19 vaccination. Lake Louise criteria were used for cardiac magnetic resonance imaging (cMRI) findings. Myocarditis cases were classified as confirmed or probable based on the Centers for Disease Control and Prevention definitions. Results: We report on 139 adolescents and young adults with 140 episodes of suspected myocarditis (49 confirmed, 91 probable) at 26 centers. Most patients were male (N=126, 90.6%) and White (N=92, 66.2%); 29 (20.9%) were Hispanic; and median age was 15.8 years (range 12.1-20.3, IQR 14.5-17.0). Suspected myocarditis occurred in 136 patients (97.8%) following mRNA vaccine, with 131 (94.2%) following the Pfizer-BioNTech vaccine; 128 (91.4%) occurred after the 2nd dose. Symptoms started a median of 2 days (range 0-22, IQR 1-3) after vaccination. The most common symptom was chest pain (99.3%). Patients were treated with nonsteroidal anti-inflammatory drugs (81.3%), intravenous immunoglobulin (21.6%), glucocorticoids (21.6%), colchicine (7.9%) or no anti-inflammatory therapies (8.6%). Twenty-six patients (18.7%) were in the ICU, two were treated with inotropic/vasoactive support, and none required ECMO or died. Median hospital stay was 2 days (range 0-10, IQR 2-3). All patients had elevated troponin I (N=111, 8.12 ng/mL, IQR 3.50-15.90) or T (N=28, 0.61 ng/mL, IQR 0.25-1.30); 69.8% had abnormal electrocardiograms and/or arrythmias (7 with non-sustained ventricular tachycardia); and 18.7% had left ventricular ejection fraction (LVEF) <55% on echocardiogram. Of 97 patients who underwent cMRI at median 5 days (range 0-88, IQR 3-17) from symptom onset, 75 (77.3%) had abnormal findings: 74 (76.3%) had late gadolinium enhancement, 54 (55.7%) had myocardial edema, and 49 (50.5%) met Lake Louise criteria. Among 26 patients with LVEF <55% on echocardiogram, all with follow-up had normalized function (N=25). Conclusions:Most cases of suspected COVID-19 vaccine myocarditis occurring in persons <21 years have a mild clinical course with rapid resolution of symptoms. Abnormal findings on cMRI were frequent. Future studies should evaluate risk factors, mechanisms, and long-term outcomes.

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Background: Coronary artery abnormalities (CAAs) still occur in patients with Kawasaki disease receiving intensified treatment with corticosteroids. We aimed to determine the risk factors of CAA development and resistance to intensified treatment in Post RAISE (Prospective Observational Study on Stratified Treatment With Immunoglobulin Plus Steroid Efficacy for Kawasaki Disease)—the largest prospective cohort of Kawasaki disease patients to date. Methods: In Post RAISE, 2648 consecutive patients with Kawasaki disease were enrolled. The present study analyzed 724 patients predicted to be intravenous immunoglobulin (IVIG) nonresponders (Kobayashi score ≥5) who received intensified treatment consisting of IVIG plus prednisolone. The association between the baseline characteristics and CAA at 1 month after disease onset was examined. The association between the baseline characteristics and treatment resistance was also investigated. Results: Maximum Z score at baseline ≥2.5 (odds ratio, 3.4 [95% CI, 1.5–7.8]), age at fever onset <1 year (odds ratio, 3.4 [95% CI, 1.6–7.4]), and nonresponsiveness to IVIG plus prednisolone treatment (odds ratio, 6.8 [95% CI, 3.3–14.0]) were independent predictors of CAA development. Nonresponsiveness to IVIG plus prednisolone was significantly associated with 8 baseline variables. Baseline total bilirubin (odds ratio, 1.4 [95% CI, 1.2–1.7]) was the only significant independent predictor other than the variables included in the Kobayashi score, enabling treatment resistance to be identified at diagnosis. The area under the ROC curve was 0.74 (95% CI, 0.69–0.79). At a cutoff point of 1.0, the sensitivity and specificity for predicting treatment resistance were 71% and 65%, respectively. Conclusions: In Post RAISE, younger age at fever onset, a larger maximum Z score at baseline, and nonresponsiveness to IVIG plus prednisolone were risk factors significantly associated with CAA development. Nonresponders were able to be identified at diagnosis based on the total bilirubin value. To prevent CAA, more intensified or adjunctive therapies using other agents, such as pulsed methylprednisolone, ciclosporin, infliximab, and Anakinra, should be considered for patients with these risk factors. Registration: URL: https://www.umin.ac.jp/ctr/ ; Unique identifier: UMIN000007133.

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