«The disease burden caused by the SARS-CoV-2 virus in the population <20 years is low compared to other age groups. Age is the main predictor of disease severity as shown by the proportion of hospitalization and death by age categories. A lower prevalence of antibodies in young children demonstrated in serology studies indicates that not only severity but also the risk of infection is age dependent.

The risk of being infected clearly depends on exposure to infected household members as the primary source of infection, but also exposure from other sources in the environment including peers in daycare/school and leisure activities. Little is known regarding socio-economic factors such as household crowding, household size and family income as risk factors for infections in young people. In the US, Afro-American or mixed race was associated with increased hospitalization risk, but underlying socio-economic factors for being infected is likely the driver for this association.
Improved knowledge of risk factors for being infected or hospitalised is relevant for mitigation and future vaccine strategies. In this nation-wide study covering the first year of the pandemic, we aimed to determine risk factors for infections and for hospitalisation in the population <20 years.

We investigate the epidemiology of SARS-CoV-2 infections in a nation-wide, population-based study covering all individuals < 20 years living in Norway. In an open cohort we include inhabitants <20 years on March 1st 2020 and children immigrated or born between March 1st 2020 and February 28th 2021. End of follow-up is February 28th 2021, age 20 years, death or emigration whichever occurs first. Non-residents (tourists, temporary workers and asylum applicants) are excluded.

Individual-level data are available from the BEREDT C19 registry, developed specifically for emergency preparedness to provide knowledge of the spread of the SARS-CoV-2 virus. In the registry the unique national identification number given to all citizens upon birth or immigration to link is used to link vital sources of information»