SARS-CoV-2 seroprevalence in children, parents and school personnel from June 2020 to April 2021: cohort study of 55 schools in Switzerland

  1. Agne Ulyte
  2. Sarah R. Haile
  3. Jacob Blankenberger
  4. Thomas Radtke
  5. Milo A. Puhan
  6. Susi Kriemler

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Abstract

BACKGROUND: Few studies have directly examined the incidence or seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in children, parents and teachers from the same school communities. This study aimed to describe SARS-CoV-2 seroprevalence within cantonal districts and school communities in children, parents and school personnel in June-September 2020 and March-April 2021 in the canton of Zürich, Switzerland. METHODS: We invited children from 55 randomly selected primary and secondary schools and 275 classes within them to participate in the Ciao Corona study in June-July 2020. Parents of the participating children and all school personnel were invited in August-September 2020. Eligible classes, parents and school personnel were tested again in March-April 2021. Venous blood was tested for SARS-CoV-2 serology. We collected sociodemographic information of the participants in online questionnaires on enrolment in the study. We excluded vaccinated adults and those with unverified vaccination status from the main analysis. Seroprevalence estimates were adjusted for test accuracy. We assessed the variability of seroprevalence within and across cantonal districts and school communities and compared it with the per capita cumulative incidence of confirmed SARS-CoV-2 infections. RESULTS: In June-September 2020, 2,473 children, 1,608 school personnel and 2,045 parents participated in the study. In June-September 2020, seroprevalence was low (4.4% to 5.8%) in all cohorts. In March-April 2021, seroprevalence in children and parents (18.1% and 20.9%) was slightly higher than in school personnel (16.9%). We observed a large variation in seroprevalence estimates of the three cohorts within and between districts and school communities, with the median ratio of children’s seroprevalence to per capita confirmed cases in district inhabitants of 3.1 (interquartile range 2.6 to 3.9). Seroprevalence was lower in children in the upper school level and their parents, but not teachers. Children’s seroprevalence was slightly higher in classes with infected main teachers and families with one infected parent and substantially higher in families with two infected parents. CONCLUSIONS: We observed similar seroprevalence in children and parents, somewhat lower in school personnel in March-April 2021 and striking variation between districts and school communities. Children’s seroprevalence was higher in classes with infected main teachers and from families with infected parents.

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  1. Version published to 10.4414/smw.2022.w30193
  2. ScreenIT

    SciScore for 10.1101/2022.01.25.22269827: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Ethicsnot detected.
    Sex as a biological variablenot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.

    Table 2: Resources

    No key resources detected.

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    However, it has several limitations. First, despite random sampling of schools and classes, children participating within classes (approximately 50%) might be somewhat (self) selected. Parents were more likely to attend testing in March-April 2021 if their child reported symptoms in 2020-2021 (at least one parent of 52% asymptomatic and 67% symptomatic children participated). However, participation was not different in parents of seropositive and seronegative children. Second, although serological tests have the advantage of capturing also the non-diagnosed SARS-CoV-2 infections, temporal and directional associations cannot be deduced. Positive serological test result could reflect an infection of up to a year ago, although antibodies are subject to some waning (14). Finally, the study was conducted when the delta or omicron variants of SARS-CoV-2 were not yet prevalent in Switzerland. Due to higher infectiousness, the associations of seroprevalence within families and classes might be different beyond the timeframe of this study. In conclusion, we observed similar seroprevalence in children and parents, and somewhat lower in school personnel in March-April 2021 in Zurich, Switzerland, and striking variation between districts and school communities. Children’s seroprevalence was higher in classes with infected main teachers and from families with infected parent(s). The class and school community trends in seroprevalence could also be driven by community transmission outside ...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    Results from scite Reference Check: We found no unreliable references.

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  3. Version published to 10.1101/2022.01.25.22269827v1 on medRxiv