We're talking about ~1:10000 odds for one specific vaccine when vaccinating young males, which is why many countries are no longer using that vaccine for this demographic. Other vaccines are closer to 1:100000, which isn't far from the myocarditis risk of an infection with COVID-19.
The study also shows that there was practically no increase in risk for the third shot (though with a fairly wide CI), so it's possible the risk may just depend on whether someone is immunonaive or not.
What we don't know is whether a vaccination would actually prevent Myocarditis in a breakthrough infection. These risks may well not be mutually exclusive. In any case, the risks are not directly comparable unless you assume 100% PCR-confirmed infection risk over six months, which is of course unrealistic.
1:100000 was in reference to the "males < 40" age bucket in the UK study linked by OP. The myocarditis risk from infection for the 12-17 age group appears to be significantly higher according to this study[1] (1:1141), which gets us quite close to the Hong Kong study incidence if we assume two shots after the first dose.
> In any case, the risks are not directly comparable unless you assume 100% PCR-confirmed infection risk over six months, which is of course unrealistic.
I do wonder how unrealistic it is with Omicron, but maybe we'll get lucky and Omicron's less likely to cause myocarditis.
The study also shows that there was practically no increase in risk for the third shot (though with a fairly wide CI), so it's possible the risk may just depend on whether someone is immunonaive or not.