From the article posted on the BMJ website yesterday.
They estimated that the rate of cardiac myocarditis after the second dose of the vaccine was 162.2 cases per million in healthy boys aged 12-15 years and 94.0 per million in those aged 16-17. For girls the rate was 13 per million in 12-15 year olds and 13.4 per million in 16-17 year olds. Nearly all (86%) of the boys affected needed some form of hospital care, the authors said. By comparison, at current infection rates the risk of a healthy adolescent being admitted to hospital within 120 days of infection in the US is estimated to be 44 per million.
Caveated again, to say the paper has not been peer reviewed and references data from second doses. But for DS's personal circumstances (elite athlete), the benefits to him, don't outweigh the risks. He wasn't especially impacted by school lockdowns/self isolation as he's at private school who ran and continue to run, a full, live, online timetable. His MH didn't particularly suffer. It's why I think in this age group, it's such a personal decision for families. His best friend is asthmatic, I would imagine he will be vaccinated, as for him, the benefits outweigh the risks.