CDC slide #7 reports 20 times higher myopericarditis than baseline for 18-24 year old males, https://www.cdc.gov/vaccines/acip/meetings/downloads/slides-...
Aug 2021 study from Yale, John Hopkins, Stanford, UCSF and others, https://pediatrics.aappublications.org/content/pediatrics/ea...
> 63 patients with a mean age of 15.6 years were included. 92% were male. All had received an mRNA vaccine and, except for one, presented following the 2nd dose. Four patients had significant dysrhythmia. 14% had mild left ventricular dysfunction on echocardiography which resolved on discharge. 88% met the diagnostic cardiac magnetic resonance (CMR) Lake Louise criteria for myocarditis.
Children and pregnant women are the two sub-populations I mentioned previously.
> Given that COVID-19 disease is far milder in the majority of children than in adults, the risk–benefit of a pediatric SARS-CoV-2 vaccine must be carefully weighed 
> The prognostic significance, long-term implications and mechanism of this myocardial injury needs to be studied further, especially as vaccination efforts are rolled out to younger children. 
> While the safety, immunogenicity, and efficacy data for the 4 authorized vaccines are reassuring so far, none of these vaccines has been systematically studied in pregnant and breastfeeding people 
> it is important to remain transparent about the lack of information, acknowledge concerns, and support those who decide to defer vaccination until more data are available 
 SARS-CoV-2 vaccine testing and trials in the pediatric population: biologic, ethical, research, and implementation challenges (Feb 2021) https://www.nature.com/articles/s41390-021-01402-z
 COVID-19 Vaccination-Associated Myocarditis in Adolescents (August 2021) https://pediatrics.aappublications.org/content/pediatrics/ea...
 SARS-CoV-2 Vaccination During Pregnancy: A Complex Decision (April 2021) https://academic.oup.com/ofid/article/8/5/ofab180/6220034