The study is divided into a Screening phase and a Follow-up phase. In the Screening phase, an obligatory polymerase chain reaction (PCR) in the nasopharyngeal swab and an optional serum antibody testing are carried out for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). An obligatory standardized questionnaire is used to evaluate symptoms and contacts, medical history and underlying conditions and the psychological effects of the Coronavirus disease 2019 (COVID-19) pandemic, as well as its effects on individual access to medical care. Children with a positive nasopharyngeal swab or antibody test, as well as their household contacts aged 0 to 18 years enter the Follow-up phase. During the Follow-up phase, blood and urine samples are taken from children for immunological analysis, HLA typing and untargeted metabolomics, enabling a broad analysis of the adaptive and innate immune response to SARS-CoV-2, as well as metabolic and genetic risk factors for infection and disease compared to age and sex-matched healthy controls. Furthermore, a repeated swab and antibody testing at 0, 3 and 6 months for children and adult household contacts is carried out to analyse household transmission of SARS-CoV-2 in children and adults and the persistence of antibodies.
