The overarching objective for this prospective cohort study of COVID-19 in adolescents is to study the long-term effects, with particular emphasis on post-infectious chronic fatigue. A total of 500 individuals with a SARS-CoV-2 positive test will be enrolled in the acute phase of COVID-19 and followed for 6 months. A total of 100 individuals with SARS-CoV-2 negative test will be included during the same time period as a control group. Investigations include autonomic, pulmonary and cognitive assessement; a questionnaire charting symptoms, emotionality, personality, loneliness, life events and demographics; and extensive biobanking including genetic markers, viable PBMC, urine, feces and hair. A subgroup of 40 SARS-CoV-2 positive and 20 SARS-CoV-2 negative individuals will also undergo detailed cardiological examination by echocardiography. Primary endpoints are fatigue at 6 months as assessed by the Chalder Fatigue Scale and post-COVID-19 syndrome cases at 6 months according to the WHO definition