The study measures infection rates and the presence of antibodies for SARS-CoV-2 (COVID-19) among in- and outpatients of all pediatric hospitals, as well as volunteers aged 0 to 18 years in Hamburg, Germany. Participants with a positive nasopharyngeal swab PCR or a positive antibody test enter the Follow-up phase of 6 months. The follow up includes a PCR and antibody testing of all household contacts at 0, 3 and 6 months, as well as laboratory testing of children to identify immunological, metabolic and genetic risk factors for infection and clinical outcome.

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.

Inclusion Criteria:

• Children or Teenagers aged 0-18 years
• Patient in one of the participating centers or volunteer in the central C19.CHILD Study Clinic
• Informed consent from parents or guardians.
• Informed consent from children >7 years (unless not capable)

Exclusion Criteria:

• Prematurity <37 weeks of gestation
• Informed consent of parents and guardians not possible in spoken word or otherwise
• Informed consent not given

1. In- and outpatients aged 0 to 18 years of all pediatric hospitals in Hamburg, Germany
2. Healthy children aged 0 to 18 years as volunteers
3. Participants of other studies or their children (Prenatal Investigation of Children's Health - PRINCE Study, Hamburg City Health Study)
4. Children, who are household contacts of SARS-CoV-2 positive study participants will directly enter the Follow-up phase

Healthy Control Group:

A group of children tested negative for SARS-CoV-2 by PCR and antibody testing will be included as control group for the immunologic, metabolic and genetic follow up. This group is recruited from participants in group 2 and 3 (above).