COVID-19 in Hospitalised Norwegian Children - Risk Factors, Outcomes and Immunology

This nation-wide, prospective cohort study of COVID-19 infection addresses three main issues: 1) Epidemiological risk factors; 2) Natural history (including immunological mechanisms and long term effects) and 3) Support of infection prevention. Also, the study focuses solely on children. Children (0-18 years of age) admitted to hospital with suspected COVID-19 are eligible (Fig. 1). Those with confirmed COVID-19 serve as cases, whereas those with non-COVID-19 serve as controls; both groups will be followed prospectively for 6 months. Three objectives/Work Packages (WPs) are defined: * In WP1, the investigators will investigate risk factors for severe outcome of the acute infection; potential risk factors include sex, age, comorbidities, initial clinical findings, infectious load, and genetic markers. * In WP2, the investigators will investigate the immunological response to acute infection, focusing on initial innate host response and its associations to inflammatory enhancement, genetic factors and clinical course. * In WP3, the investigators will investigate the prevalence and risk factors of long-lasting complication, in particular the development of post-infectious chronic fatigue