SARS-CoV 2CiaoCoronaNCT04448717

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

An observational study of SARS-CoV 2 and COVID-19, run by University of Zurich at 1 site in Switzerland.

Completed

Finished. The study has ended and is not enrolling. Results may be posted on the official record.

Trial summary

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… Read more about this study

Who is it for?: Ages 5 years and olderHealthy volunteers can take part
Conditions the study is for: SARS-CoV 2, COVID-19
What is being tested?: COVID-19 Antibody testing
How many people: 4,250 participants
Where: 1 siteSwitzerland
Study dates: 16 Jun 2020to 20 Jul 2022
Phase: Observational
Are there results?: None posted in the registry

Key requirements

Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.

Ages 5 years and older
All sexes
Healthy volunteers accepted
Child, Adult, Older adult

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.

Who may be able to join

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.

Who cannot join

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.

Trial locations and contacts

1 site in 1 country.

Switzerland1 site

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

Other trials in Switzerland

About this study

Official title: 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.

Read the 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.

Conditions: SARS-CoV 2, COVID-19
Being tested: COVID-19 Antibody testing
Keywords: Seroprevalence, Seroepidemiology, School children, Switzerland, Schools, Households, Students
Medical subject headings: COVID-19

What participants receive

What participants receive. In a randomised study each person is assigned to one group by chance.

COVID-19 Antibody testingDiagnostic test
COVID-19 Antibody testing in venous blood and/or saliva samples.

Study groups in NCT04448717
Study group	Role	What they receive
Children and adolescents		Children and adolescents in primary and secondary schools (aimed sample size: 2500) Receives: Diagnostic Test: COVID-19 Antibody testing
Parents		Parents of participating children (aimed sample size: 3000) Receives: Diagnostic Test: COVID-19 Antibody testing
School personnel		School personnel (teaching, administrative, maintenance, etc.) (aimed sample size: 2500) Receives: Diagnostic Test: COVID-19 Antibody testing

What is being measured

The primary outcome is the main question the study is designed to answer.

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.
Measured: 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.
Measured: 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.
Measured: 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.
Measured: 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.
Measured: Month 24-30

Secondary outcomes (16)

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.
Measured: 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.
Measured: 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.
Measured: 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.
Measured: 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.
Measured: 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.
Measured: 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.
Measured: 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.
Measured: 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.
Measured: 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.
Measured: 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.
Measured: 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.
Measured: 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.
Measured: 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.
Measured: 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.
Measured: 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.
Measured: within 36 months of follow-up

Timeline

From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.

16 Jun 202020 Jul 2022

First posted26 Jun 2020
Study start16 Jun 2020
Primary completion20 Jul 2022
Study completion20 Jul 2022

Resources

Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
Publications (14)Papers the sponsor has linked to this study.
Other trials for SARS-CoV 2Studies of the same condition, open and under way.
More trials run by University of ZurichThe sponsor's other registered studies.
What the trial phases meanHow a treatment moves from first tests in people to approval.

More details

For doctors and researchers: how the study is designed, who runs it, and its registry IDs.

Study design

Study type: Observational
Observational model: Cohort
Time perspective: Prospective
Enrolment: 4,250 participants (actual)

IDs, dates and publications

ClinicalTrials.gov ID: NCT04448717
Sponsor's protocol ID: 2020-01336
Acronym: CiaoCorona
Status last verified: Mar 2025
First submitted: 18 Jun 2020
Last updated: 3 Apr 2025
Results posted: No
Data monitoring committee: No
FDA-regulated drug: No
FDA-regulated device: No
Individual data sharing: Undecided: 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.

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.
PubMed 33731327
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.
PubMed 34264266
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.
PubMed 35748765
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.
PubMed 36158782
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.
PubMed 34485200
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.
PubMed 33063141
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.
PubMed 37538234
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.
PubMed 38411717
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.
PubMed 36787493
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.
PubMed 34312201
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.
PubMed 33796490
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.
PubMed 38012137
Raineri A, Rueegg S, Zimmermann P, Regamey N, Benden C, Haile SR, Ulyte A, Puhan MA, Kriemler S, Radtke T. Long COVID in children and adolescents: results from three cross-sectional school-based cohorts with adjudication. Swiss Med Wkly. 2025 Oct 20;155:4337. doi: 10.57187/s.4337.
PubMed 41114667
Haile SR, Peralta GP, Adams M, Bharadwaj AN, Bassler D, Moeller A, Natalucci G, Radtke T, Kriemler S. Health-related quality of life in children and adolescents born very preterm and its correlates: a cross-sectional study. BMJ Paediatr Open. 2024 Oct 10;8(1):e002885. doi: 10.1136/bmjpo-2024-002885.
PubMed 39389623

Want to know more?

The sponsor has not listed a contact. The official record may have more details.

Talk to your doctor first and take this page with you. Only the study team can confirm whether you can join.

Questions to ask the study team

What is the study trying to find out?
What would I need to do, and how often would I visit?
Could I receive a placebo instead of the treatment?
What are the possible risks and benefits for me?
Will it cost me anything? Are travel or time paid for?
Can I keep seeing my own doctor during the study?
What happens when the study ends?

See locations

RecruitingPhase 3
Randomized, Embedded, Multifactorial Adaptive Platform Trial for Community- Acquired Pneumonia
Respiratory Tract Diseases, Influenza (Pandemic)
Not yet recruiting
Effect of MxA Guidance on Antiviral Treatment in Respiratory Viral Infections
Respiratory Viral Infections, Influenza
Recruiting
Effectiveness of Transcranial Direct Current in Patients With Persistent COVID-19 With Headaches and Chronic Pain.
COVID-19, Long COVID
Active, not recruiting
Clinical Validation of the NowFuture Digital Flu / COVID Test in Anterior Nasal Samples for Over-the-Counter (OTC) Use in Australia
SARS CoV 2 Infection, Influenza A Virus Infection
RecruitingObservational study
Determinants of SARS (Severe Acute Respiratory Syndrome)-COV2 (COVID-19) Persistence After Convalescence
COVID-19, Corona Virus Infection

All SARS-CoV 2 trials

Study at a glance

From the registry record, last updated by the sponsor on 3 Apr 2025. Recruitment status is as the sponsor reported it: confirm with the study team.

Official title: Seroprevalence of SARS-CoV-2 Antibodies and Development of Immunity in a Public School Population - a Population-based Observational Study to Inform Policy Making
ClinicalTrials.gov ID: NCT04448717
Acronym / sponsor ID: CiaoCorona / 2020-01336
Conditions: SARS-CoV 2, COVID-19
Keywords: Seroprevalence, Seroepidemiology, School children, Switzerland, Schools, Households, Students
Study type: Observational
Recruitment status: Completed
Enrolment: 4,250 participants (actual)
Lead sponsor: University of ZurichUniversity, hospital or other
Collaborators: Swiss School of Public Health (SSPH+)
Study start: 16 Jun 2020 (actual)
Primary completion: 20 Jul 2022 (actual)
Study completion: 20 Jul 2022 (actual)
First posted: 26 Jun 2020 (actual)
Results: Not posted in the source record

Clinical summary

The research question as the sponsor registered it. This describes what the study plans to test, not what it found.

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.

Detailed description

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 design

Observational model: Cohort
Time perspective: Prospective
Number of arms: 3

Arm	Type	Receives
Children and adolescents	–	Diagnostic Test: COVID-19 Antibody testingChildren and adolescents in primary and secondary schools (aimed sample size: 2500)
Parents	–	Diagnostic Test: COVID-19 Antibody testingParents of participating children (aimed sample size: 3000)
School personnel	–	Diagnostic Test: COVID-19 Antibody testingSchool personnel (teaching, administrative, maintenance, etc.) (aimed sample size: 2500)

Who may qualify

Ages: 5 years and older
Sex: All
Healthy volunteers: Accepted
Age groups: Child, Adult, Older adult
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.

Key inclusion criteria (7 listed)

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:
Informed consent of parents or legal guardians and children, or the adult participant.

Key exclusion criteria (5 listed)

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.

Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.

Interventions

Intervention	Type	Arms
COVID-19 Antibody testingCOVID-19 Antibody testing in venous blood and/or saliva samples.	Diagnostic test	Children and adolescents, Parents, School personnel

Primary outcome

Seroprevalence of SARS-CoV-2 IgG, IgM and/or IgA antibodies
Time frame: at inclusion
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.
Seroprevalence of SARS-CoV-2 IgG, IgM and/or IgA antibodies
Time frame: Month 4-5
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.
Seroprevalence of SARS-CoV-2 IgG, IgM and/or IgA antibodies
Time frame: Month 8-9
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.
Seroprevalence of SARS-CoV-2 IgG antibodies
Time frame: Month 17-18
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.
Seroprevalence of SARS-CoV-2 IgG antibodies
Time frame: Month 24-30
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.

16 secondary outcomes

Presence of self-reported symptoms
Time frame: at inclusion
Proportion of seropositive children reporting COVID-19 related symptoms from January 2020
Time frame: at inclusion
Presence of self-reported symptoms
Time frame: within 36 months of follow-up
Incidence of symptoms in initially seropositive participants
Time frame: within 36 months of follow-up
Proportion of participants, seronegative at inclusion, with symptoms in the follow-up
Time frame: within 36 months of follow-up
Presence of risk factors for infection at inclusion (assessment via custom questionnaire)
Time frame: at inclusion
Presence of risk factors for infection during follow-up (assessment via custom questionnaire)
Time frame: within 36 months of follow-up
Self-reported lifestyle changes of participants at inclusion
Time frame: at inclusion
Self-reported lifestyle changes of participants during follow-up
Time frame: within 36 months of follow-up
Self-reported mental well-being (KINDL questionnaire)
Time frame: within 36 months of follow-up
Self-reported mental well-being (HBSC questionnaire)
Time frame: within 36 months of follow-up
Self-reported quality of life (KINDL questionnaire)
Time frame: within 36 months of follow-up
Prevalence of seropositive SARS-Cov-2 clusters in schools at inclusion
Time frame: at inclusion
Incidence of seropositive SARS-Cov-2 clusters in schools during the follow-up
Time frame: within 36 months of follow-up
Change in seropositive participants within school or class, depending on the initial proportion of seropositive participants
Time frame: within 36 months of follow-up
Effect of risk factors and preventive measures on SARS-CoV-2 infection incidence within schools
Time frame: within 36 months of follow-up

Results and safety

The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.

Research links

Official record on ClinicalTrials.govLast updated by the sponsor 3 Apr 2025.
Background: PubMed 33731327Ulyte 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.
Background: PubMed 34264266Radtke 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.
Background: PubMed 35748765Ammann 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.
Background: PubMed 36158782Peralta 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.
Background: PubMed 34485200Blankenberger 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.
Background: PubMed 33063141Ulyte 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.
Background: PubMed 37538234Haile 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.
Background: PubMed 38411717Haile 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.
Background: PubMed 36787493Haile 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.
Background: PubMed 34312201Ulyte 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.
Background: PubMed 33796490Kriemler 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.
Results publication: PubMed 38012137Raineri 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.
Individual participant dataSharing planned: Undecided. 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.

Related trials for SARS-CoV 2

RecruitingPhase 3
Randomized, Embedded, Multifactorial Adaptive Platform Trial for Community- Acquired Pneumonia
Respiratory Tract Diseases, Influenza (Pandemic)
Not yet recruiting
Effect of MxA Guidance on Antiviral Treatment in Respiratory Viral Infections
Respiratory Viral Infections, Influenza
Recruiting
Effectiveness of Transcranial Direct Current in Patients With Persistent COVID-19 With Headaches and Chronic Pain.
COVID-19, Long COVID
Active, not recruiting
Clinical Validation of the NowFuture Digital Flu / COVID Test in Anterior Nasal Samples for Over-the-Counter (OTC) Use in Australia
SARS CoV 2 Infection, Influenza A Virus Infection
RecruitingObservational study
Determinants of SARS (Severe Acute Respiratory Syndrome)-COV2 (COVID-19) Persistence After Convalescence
COVID-19, Corona Virus Infection

Referral and contact

AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.

Susi Kriemler, Prof. principal investigator

University of Zurich

1 site in 1 country: see every site and its status.

Questions about this trial

What is this clinical trial studying?

An observational study of SARS-CoV 2 and COVID-19, run by University of Zurich at 1 site in Switzerland.

The full registered description is in the About this study section and the official record.

Who may be eligible to take part?

The sponsor lists 7 inclusion and 5 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.

Is this clinical trial currently recruiting?

The record says: finished, as of the sponsor's last update on 3 Apr 2025. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 1 site in Switzerland. Whether a site is taking part right now should be confirmed with that site. See every site.

What are the possible benefits and risks?

They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.

Are results available for this study?

The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.

How can a doctor refer a patient or contact the research team?

The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.

What does the primary outcome measure?

Seroprevalence of SARS-CoV-2 IgG, IgM and/or IgA antibodies (time frame: at inclusion). The study lists 5 primary outcomes in all. It is what the study was designed to measure, not a finding.

Where can I read the original study information?

On the ClinicalTrials.gov record for NCT04448717, which also lists 14 linked publications.

Does a listing mean the treatment is approved or proven to work?

No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.

How often is this information updated?

AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 3 Apr 2025.