Transmission of SARS-CoV-2 in Norwegian schools during academic year 2020-21: population wide, register based cohort study

  1. T A Rotevatn
  2. Vilde Bergstad Larsen
  3. Tone Bjordal Johansen
  4. Elisabeth Astrup
  5. Pål Surén
  6. Margrethe Greve-Isdahl
  7. Kjetil Elias Telle

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Abstract

To assess the risk of transmission of SARS-CoV-2 in schools in Norway mainly kept open during the covid-19 pandemic in the academic year 2020-21.

Design

Population wide, register based cohort study.

Setting

Primary and lower secondary schools in Norway open during the academic year 2020-21, with strict infection prevention and control measures in place, such as organisation of students into smaller cohorts. Contact tracing, quarantine, and isolation were also implemented, and testing of students and staff identified as close contacts.

Participants

All students and educational staff in primary and lower secondary schools in Norway, from August 2020 to June 2021.

Main outcome measures

Overall attack rate of SARS-CoV-2 transmission (AR14) was defined as the number of individuals (among students, staff, or both) in the school with covid-19, detected within 14 days of the index case, divided by the number of students and staff members in the school. AR14 to students (attack rates from all index cases to students only) and AR14 to school staff (attack rates from all index cases to staff members only) were also calculated. These measures for student and school staff index cases were also calculated separately to explore variation in AR14 based on the characteristics of the index case.

Results

From August 2020 to June 2021, 4078 index cases were identified; 3220 (79%) students and 858 (21%) school staff. In most (2230 (55%)) schools with an index case, no subsequent individuals with covid-19 were found within 14 days; in 631 (16%) schools, only one more individual with covid-19 within 14 days was found. Overall, AR14 was 0.33% (95% confidence interval 0.32% to 0.33%). When restricting index cases and subsequent individuals with covid-19 to students born in the same year, AR14 to students (0.56-0.78%) was slightly higher.

Conclusions

Regarding the number of people infected with SARS-CoV-2 among students and staff, these results suggest that schools were not an important setting for transmission of the virus in Norway during the covid-19 pandemic in the academic year 2020-21.

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  1. Version published to 10.1136/bmjmed-2021-000026
  2. ScreenIT

    SciScore for 10.1101/2021.10.04.21264496: (What is this?)

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

    Table 1: Rigor

    EthicsIRB: Ethical approval: The emergency preparedness register, BEREDT C19, was established according to the Health Preparedness Act §2-4 and the project was approved by the Ethics Committee of South-East Norway (9th March 2021, #198964).
    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:
    Limitations of the study: To our knowledge, this is the first study of transmission rates of COVID-19 in schools using data representative for an entire nation, covering a full academic year. There are, however, certain limitations associated with our analysis. First, since transmission is far more likely to occur within the family than in school or other public domains (1, 15, 16), transmission between siblings attending the same school may have led to us overestimating SAR14. Lack of data on whether secondary cases were actually infected in school or elsewhere, may also have led to overestimation. However, if we are in fact overestimating SAR14, this would only strengthen our finding that Norwegian primary and lower secondary schools have not been important arenas for SARS-CoV-2 transmission. Second, the registry data did not include information on which students and educational staff at the school were actual close contacts. Thus, we did not have the data necessary to estimate secondary attack rates among close contacts. Therefore, the aim of this study was not to estimate effects among close contacts, but to generate knowledge on general transmission in primary and lower secondary schools. The relatively high testing rates compared to transmission rates following the detection of an index case, indicate that most true secondary cases were captured in our data. Students in the same grade at the same school, are more likely to be close contacts than students at the same sch...

    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.

    About SciScore

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  3. Version published to 10.1101/2021.10.04.21264496 on medRxiv