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

Seroprevalence of SARS-CoV-2 Antibodies and Development of Immunity in a Public School Population - a Population-based Observational Study to Inform Policy Making

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.

Study Overview

• Status: Completed
• Conditions: COVID-19; SARS-CoV 2
• Intervention / Treatment: Diagnostic test: COVID-19 Antibody testing

Detailed Description

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.

• Study Type: Observational
• Enrollment (Actual): 4250

Contacts and Locations

Study Locations

• Switzerland
  • Zurich, Switzerland, 8001
    • Epidemiology, Biostatistics and Prevention Institute (EBPI), University of Zurich

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 5 years and older (Child, Adult, Older Adult)
• Accepts Healthy Volunteers: Yes

• Sampling Method: Probability Sample

Study Population

School children, attending grades 1 to 9 in a public or private school in the Canton of Zurich, Switzerland.

Parents of participating children. School personnel of participating schools.

Description

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.

Study Plan

How is the study designed?

Design Details

• Observational Models: Cohort
• Time Perspectives: Prospective

Number of groups / cohorts

3

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Children and adolescents; Children and adolescents in primary and secondary schools (aimed sample size: 2500)	Diagnostic test: COVID-19 Antibody testing; COVID-19 Antibody testing in venous blood and/or saliva samples.
Parents; Parents of participating children (aimed sample size: 3000)	Diagnostic test: COVID-19 Antibody testing; COVID-19 Antibody testing in venous blood and/or saliva samples.
School personnel; School personnel (teaching, administrative, maintenance, etc.) (aimed sample size: 2500)	Diagnostic test: COVID-19 Antibody testing; COVID-19 Antibody testing in venous blood and/or saliva samples.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Seroprevalence of SARS-CoV-2 IgG, IgM and/or IgA antibodies	Seroprevalence of SARS-CoV-2 IgG, IgM and/or IgA antibodies in randomly selected 5- to 16-year-old population of school-children, their parents, and school personnel, after the peak phase of the first major wave shortly after re-opening of schools in the canton of Zürich, Switzerland.	at inclusion
Seroprevalence of SARS-CoV-2 IgG, IgM and/or IgA antibodies	Seroprevalence of SARS-CoV-2 IgG, IgM and/or IgA antibodies in randomly selected 5- to 16-year-old population of school-children and school personnel after 4-5 after recruitement in the canton of Zürich, Switzerland.	Month 4-5
Seroprevalence of SARS-CoV-2 IgG, IgM and/or IgA antibodies	Seroprevalence of SARS-CoV-2 IgG, IgM and/or IgA antibodies in randomly selected 5- to 16-year-old population of school-children and school personnel after 8-9 months after recruitment in the canton of Zürich, Switzerland.	Month 8-9
Seroprevalence of SARS-CoV-2 IgG antibodies	Seroprevalence of SARS-CoV-2 IgG antibodies in randomly selected 5- to 16-year-old population of school-children and school personnel after 17-18 months after recruitment in the canton of Zürich, Switzerland.	Month 17-18
Seroprevalence of SARS-CoV-2 IgG antibodies	Seroprevalence of SARS-CoV-2 IgG antibodies in randomly selected 5- to 16-year-old population of school-children and school personnel after 24-30 months after recruitment in the canton of Zürich, Switzerland.	Month 24-30

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Presence of self-reported symptoms	Presence of symptoms (from January 2020) suggestive of a common cold, influenza and similar upper respiratory tract infections prior to the first study visit.	at inclusion
Proportion of seropositive children reporting COVID-19 related symptoms from January 2020	Proportion of seropositive children reporting symptoms suggestive of a common cold, influenza and similar upper respiratory tract infections between January 2020 and first study visit.	at inclusion
Presence of self-reported symptoms	Presence of symptoms (from January 2020) suggestive of a common cold, influenza and similar upper respiratory tract infections during the follow-up.	within 36 months of follow-up
Incidence of symptoms in initially seropositive participants	Incidence of self-reported symptoms and SARS-CoV-2 infections after the first study visit in initially seropositive participants.	within 36 months of follow-up
Proportion of participants, seronegative at inclusion, with symptoms in the follow-up	Proportion of seronegative participants of the first investigation wave who will self-report symptoms and infection with SARS-CoV-2.	within 36 months of follow-up
Presence of risk factors for infection at inclusion (assessment via custom questionnaire)	Potential personal (socioeconomic characteristics, health status, presence of infection in family, personal hygiene and social distancing measures) and school-level (implementation of informational, social distancing and hygiene measures at school) risk and preventive factors for SARS-CoV-2 infection prior to the study. Questionnaire includes HBSC and custom questions.	at inclusion
Presence of risk factors for infection during follow-up (assessment via custom questionnaire)	Potential personal (socioeconomic characteristics, health status, presence of infection in family, personal hygiene and social distancing measures) and school-level (implementation of informational, social distancing and hygiene measures at school) risk and preventive factors for SARS-CoV-2 infection during the follow-up. Questionnaire includes HBSC and custom questions.	within 36 months of follow-up
Self-reported lifestyle changes of participants at inclusion	Changes in lifestyle during the lock-down, compared to prior to it: frequency and duration (in hours, daily) of physical activity, duration (in hours, daily) of sleep, duration of screen-based media-use (in hours, daily). This outcome is measured only in the children population.	at inclusion
Self-reported lifestyle changes of participants during follow-up	Changes in lifestyle after the lock-down and school reopening, compared to during lock-down: frequency and duration (in hours, daily) of physical activity, duration (in hours, daily) of sleep, duration of screen-based media-use (in hours, daily). This outcome is measured only in the children population.	within 36 months of follow-up
Self-reported mental well-being (KINDL questionnaire)	Changes over the study time in mental well-being of the participants during and after the lock-down: frequency scale (never/rarely/sometimes/often/always) of self-reported stress, anxiety, self-confidence feelings in the last 7 days. This outcome is measured only in the children population.	within 36 months of follow-up
Self-reported mental well-being (HBSC questionnaire)	Changes over the study time in mental well-being of the participants during and after the lock-down: frequency scale (daily/weekly/monthly/rarer) of self-reported sadness, anxiety and sleeping problems (HBSC questionnaire question on mental well-being). This outcome is measured only in the children population.	within 36 months of follow-up
Self-reported quality of life (KINDL questionnaire)	Changes over the study time in quality-of-life of the participants during and after the lock-down: frequency scale (never/rarely/sometimes/often/always) assessment of self-reported positive and negative social interactions with family, friends and in the school environment in the last 7 days. This outcome is measured only in the children population.	within 36 months of follow-up
Prevalence of seropositive SARS-Cov-2 clusters in schools at inclusion	Prevalence of clusters of seropositive children, adolescents, and school personnel within schools and classes at baseline.	at inclusion
Incidence of seropositive SARS-Cov-2 clusters in schools during the follow-up	Incidence of clusters of seropositive children, adolescents, and school personnel within schools and classes during the follow-up.	within 36 months of follow-up
Change in seropositive participants within school or class, depending on the initial proportion of seropositive participants	Impact of the number of children/adolescents and school personnel at a specific period (baseline, at the second and third testing date) within a school or class to the subsequent seropositivity within the same group.	within 36 months of follow-up
Effect of risk factors and preventive measures on SARS-CoV-2 infection incidence within schools	Incidence of seropositive children and school personnel according to potential risk factors and preventive measures for SARS-CoV-2 infection within schools.	within 36 months of follow-up

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Evolution of cellular immunity over time	Cellular immunity (T & B cells) in a subsample of previously antibody positive and antibody negative (controls) children.	within 36 months of follow-up
Long COVID	Self-reported symptoms compatible with Long COVID (i.e., >3months) in seropositive versus seronegative children. Symptoms adapted from International Severe Acute Respiratory and emerging Infection Consortium (ISARIC).	within 36 months of follow-up

Collaborators and Investigators

• Sponsor: University of Zurich
• Collaborators: Swiss School of Public Health (SSPH+)
• Investigators: Principal Investigator: Susi Kriemler, Prof., University of Zurich

Publications and helpful links

General Publications

• Ulyte A, Radtke T, Abela IA, Haile SR, Berger C, Huber M, Schanz M, Schwarzmueller M, Trkola A, Fehr J, Puhan MA, Kriemler S. Clustering and longitudinal change in SARS-CoV-2 seroprevalence in school children in the canton of Zurich, Switzerland: prospective cohort study of 55 schools. BMJ. 2021 Mar 17;372:n616. doi: 10.1136/bmj.n616.
• Radtke T, Ulyte A, Puhan MA, Kriemler S. Long-term Symptoms After SARS-CoV-2 Infection in Children and Adolescents. JAMA. 2021 Jul 15;326(9):869-71. doi: 10.1001/jama.2021.11880. Online ahead of print.
• Ammann P, Ulyte A, Haile SR, Puhan MA, Kriemler S, Radtke T. Perceptions towards mask use in school children during the SARS-CoV-2 pandemic: descriptive results from the longitudinal Ciao Corona cohort study. Swiss Med Wkly. 2022 Apr 20;152:w30165. doi: 10.4414/smw.2022.w30165. eCollection 2022 Apr 11.
• Peralta GP, Camerini AL, Haile SR, Kahlert CR, Lorthe E, Marciano L, Nussbaumer A, Radtke T, Ulyte A, Puhan MA, Kriemler S. Lifestyle Behaviours of Children and Adolescents During the First Two Waves of the COVID-19 Pandemic in Switzerland and Their Relation to Well-Being: An Observational Study. Int J Public Health. 2022 Sep 8;67:1604978. doi: 10.3389/ijph.2022.1604978. eCollection 2022.
• Blankenberger J, Haile SR, Puhan MA, Berger C, Radtke T, Kriemler S, Ulyte A. Prediction of Past SARS-CoV-2 Infections: A Prospective Cohort Study Among Swiss Schoolchildren. Front Pediatr. 2021 Aug 16;9:710785. doi: 10.3389/fped.2021.710785. eCollection 2021.
• Ulyte A, Radtke T, Abela IA, Haile SR, Braun J, Jung R, Berger C, Trkola A, Fehr J, Puhan MA, Kriemler S. Seroprevalence and immunity of SARS-CoV-2 infection in children and adolescents in schools in Switzerland: design for a longitudinal, school-based prospective cohort study. Int J Public Health. 2020 Dec;65(9):1549-1557. doi: 10.1007/s00038-020-01495-z. Epub 2020 Oct 15.
• Haile SR, Gunz S, Peralta GP, Ulyte A, Raineri A, Rueegg S, Yasenok V, Radtke T, Puhan MA, Kriemler S. Health-Related Quality of Life and Adherence to Physical Activity and Screen Time Recommendations in Schoolchildren: Longitudinal Cohort Ciao Corona. Int J Public Health. 2023 Jul 19;68:1606033. doi: 10.3389/ijph.2023.1606033. eCollection 2023.
• Haile SR, Peralta GP, Raineri A, Rueegg S, Ulyte A, Puhan MA, Radtke T, Kriemler S. Determinants of health-related quality of life in healthy children and adolescents during the COVID-19 pandemic: Results from a prospective longitudinal cohort study. Eur J Pediatr. 2024 May;183(5):2273-2283. doi: 10.1007/s00431-024-05459-w. Epub 2024 Feb 27.
• Haile SR, Raineri A, Rueegg S, Radtke T, Ulyte A, Puhan MA, Kriemler S. Heterogeneous evolution of SARS-CoV-2 seroprevalence in school-age children: Results from the school-based cohort study Ciao Corona in November-December 2021 in the canton of Zurich. Swiss Med Wkly. 2023 Jan 30;153:40035. doi: 10.57187/smw.2023.40035.
• Ulyte A, Radtke T, Abela IA, Haile SR, Blankenberger J, Jung R, Capelli C, Berger C, Frei A, Huber M, Schanz M, Schwarzmueller M, Trkola A, Fehr J, Puhan MA, Kriemler S. Variation in SARS-CoV-2 seroprevalence across districts, schools and classes: baseline measurements from a cohort of primary and secondary school children in Switzerland. BMJ Open. 2021 Jul 26;11(7):e047483. doi: 10.1136/bmjopen-2020-047483.
• Kriemler S, Ulyte A, Ammann P, Peralta GP, Berger C, Puhan MA, Radtke T. Surveillance of Acute SARS-CoV-2 Infections in School Children and Point-Prevalence During a Time of High Community Transmission in Switzerland. Front Pediatr. 2021 Mar 16;9:645577. doi: 10.3389/fped.2021.645577. eCollection 2021.
• Raineri A, Radtke T, Rueegg S, Haile SR, Menges D, Ballouz T, Ulyte A, Fehr J, Cornejo DL, Pantaleo G, Pellaton C, Fenwick C, Puhan MA, Kriemler S. Persistent humoral immune response in youth throughout the COVID-19 pandemic: prospective school-based cohort study. Nat Commun. 2023 Nov 27;14(1):7764. doi: 10.1038/s41467-023-43330-y.

Helpful Links

• Study website with information for potential participants and media.

Study record dates

Study Major Dates

• Study Start (Actual): June 16, 2020
• Primary Completion (Actual): July 20, 2022
• Study Completion (Actual): July 20, 2022

Study Registration Dates

• First Submitted: June 18, 2020
• First Submitted That Met QC Criteria: June 25, 2020
• First Posted (Actual): June 26, 2020

Study Record Updates

• Last Update Posted (Actual): April 3, 2025
• Last Update Submitted That Met QC Criteria: March 31, 2025
• Last Verified: March 1, 2025

More Information

Terms related to this study

• Keywords: Schools; Students; Households; Seroprevalence; Seroepidemiology; School children; Switzerland
• Additional Relevant MeSH Terms: Respiratory Tract Infections; Infections; RNA Virus Infections; Virus Diseases; Respiratory Tract Diseases; Lung Diseases; Pneumonia, Viral; Pneumonia; Coronavirus Infections; Coronaviridae Infections; Nidovirales Infections; COVID-19; Immunologic Factors; Physiological Effects of Drugs; Antibodies
• Other Study ID Numbers: 2020-01336

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED
• IPD Plan Description: Sensitive clinical data from vulnerable population (children) will be collected. Therefore, it is not yet decided, if it will be possible to share IPD while preserving participant autonomy and privacy.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No