The overarching objective for this prospective cohort study on COVID-19 in adolescents is to study the long-term effects, with particular emphasis on post-infectious chronic fatigue. We hypothesise that adolescents/young adults having undergone COVID-19 has a higher prevalence of chronic fatigue long after the acute infectious event; furthermore, that risk factors for chronic fatigue encompass a complex mixture of genetic vulnerability and psychosocial factors.