Taken and translated from THL's website[1] (Finnish Institute for Healt and Welfare ) "in its study, THL has examined the incidence of myocardial inflammation requiring hospitalization in different age groups. In boys and men aged 12–39 years, a total of 6 cases of myocarditis have been reported in Finland per 381,000 doses of Comirnaty and less than 5 cases per less than 49,000 doses of Spikevax in Finland. A total of less than five cases of myocarditis have been reported in girls and women of the same age, and the prevalence of myocarditis in women and girls after vaccination has not differed from that normally seen in the general population."

The study is still ongoing in Finland, but as the early results seem to match with the other nordic countries the limitation has been placed.

[1] (Page is only in Finnish still as it was written today). https://thl.fi/fi/-/thl-ohjeistaa-tarjoamaan-alle-30-vuotiai...