COVID-19: Longitudinal Study of Seroprevalence of SARS-CoV-2 Antibodies and Development of Immunity in School Children

There is a lack of knowledge about how many children are infected with SARS-CoV-2, how often they are asymptomatic, and how long the immunity persists.

The main purpose of this study is to measure antibodies to SARS-CoV-2, symptoms, and risk factors in a representative cohort of children and adolescents in the canton of Zurich, Switzerland, shortly after re-opening of the school system and thereafter. The study also investigates antibodies to SARS-CoV-2 in parents of the children and school personnel.

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 Zürich, 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, February/March 2021, November/December 2021, and again in the second half of 2022. The detailed time plan including possible further assessments will be defined depending on the evolution of the pandemic (e.g., 2023). 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. Further testing of adults is not planned.

In different subpopulations, further in-depth analysis of immunity markers will be performed in the future.

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.

Eligibility Criteria:
Inclusion Criteria:

* Any school child residing in Switzerland aged 5 years or older and attending a consenting to participate public or private school that hosts classes of interest (grade 1 through 9) in the canton of Zürich.
* Parents of participating children.
* Personnel employed in the participating schools.
* No acute respiratory and SARS-CoV-2 infection:

  * In case of unknown respiratory infection, no presence of symptoms for at least 48 hours.
  * In case of confirmed SARS-CoV-2 infection: inclusion at the earliest 21 days from PCR-positive diagnosis after the onset of potential symptoms and no presence of symptoms for at least 48 hours (according to Standard of Care).
* Informed consent of parents or legal guardians and children, or the adult participant.

Exclusion Criteria:

* No informed consent by schools or children, or the adult participant.
* Schools with \<40 students in one of the sampled grades (1, 2, 4, 5, 7, or 8).
* Children of Kindergarten age and younger.
* Suspicion of acute COVID-19 infection.
* Special need schools.