The role of children and adolescents in the transmission of SARS-CoV-2 remains highly unclear and has been a key question since the early days of the pandemic. It has important consequences for policy decisions, especially concerning the opening of the schools, sport facilities and intergenerational contacts. However, the information on true infection rate and seroprevalence of SARS-CoV-2 is not known in children in Switzerland (and globally), as testing was limited to risk groups and those with SARS-CoV-2 coronavirus disease 2019 (COVID-19) related symptoms. In addition, indications for testing were not uniform and handled heterogeneously. Hence, it is not known whether children are less frequently infected or simply less symptomatic.

This study builds up a system to monitor the seroprevalence of SARS-CoV-2 in children and adolescents who attend school in the canton of Zrich, Switzerland. The investigators aim to assess children of randomly selected primary and secondary schools during the first weeks of re-entering school from all districts of the canton of Zurich in June and July 2020, after the temporary closure due to COVID-19 pandemic, and again in October/November 2020 and February/March 2021. A follow-up capturing health status, symptoms and behaviors over time is important, since it is currently under investigation whether persons may be at risk for reinfection. Thus, a longitudinal assessment is crucial to determine the extent and duration of immunity.

In addition, the seroprevalence of SARS-CoV-2 in the parents of the participating children will be tested in August/September 2020, to examine clusters of infections in households. Seroprevalence of SARS-CoV-2 in school personnel will be tested in August/September 2020 and subsequently in October/November 2020 and February/March 2021, to examine temporal changes in the seroprevalences in the whole school community.

This study complements the ongoing coordinated efforts of seroprevalence studies in adults in Switzerland, through the Swiss School of Public Health (SSPH+) coordinated CORONA IMMUNITAS studies.