1. Our take

    This was a cross-sectional study, available as a preprint and thus not yet peer reviewed, conducted in November 2020, studying SARS-CoV-2 transmission among 24 randomly selected Berlin, Germany school classes and their connected households. Among students, infection prevalence was 2.7% (9/338). Among staff and household members, infection prevalence was 1.4% (2/140) and 2.3% (14/611), respectively. There were no secondary infections detected in school settings one week after initial testing; the attack rate among household contacts was 1.1%. This study is promising in that it shows that school-based transmission was low , even during a peak transmission period. Still, results should be interpreted with caution as they represent a single, very brief time period.

    Study design

    cross-sectional

    Study population and setting

    Between November 2 and 16, 2020, the initial peak of Germany’s second wave, SARS-CoV-2 transmission was studied among 24 randomly selected Berlin school classes (one class per 24 schools; classes were selected from grades 3-5 and 9-12) and their connected households. Both RT-PCR (SARS-CoV-2 infection) and ELISA tests (anti-SARS-CoV-2-IgG) were performed on oro-nasopharyngeal swabs and finger-prick blood samples from all students and staff. For all household contacts, self-swabs were collected, and they provided finger-prick samples at mobile clinics setup at school. A digital questionnaire was completed by all participants two days prior to the study visit day. Infection prevention and control measures happening in the schools were documented. In any classes with identified SARS-CoV-2 infection, school attendees and household members were re-tested one week later using self-swabs for data collection.

    Summary of main findings

    The study was made up of 1119 participants (352 students, 142 staff, and 625 household members). All schools had signs of hand hygiene, soap and water in restrooms, and air ventilation at least three times per day. 15 of the 24 schools (65%) did not have an obligatory facemask obligation within the classroom, but all had one for interaction outside of the classroom. Among students, infection prevalence was 2.7% (95% CI: 1.2-5.0%; n= 9/338). Among staff and household members, infection prevalence was 1.4% (0.2-5.1%; 2/140) and 2.3% (1.2-3.8%; n=14/611), respectively. Among students, IgG antibodies were detected in 2.0% (0.8-4.1%; n=7/347) of samples. Among staff and household members, IgG antibodies were detected in 1.4% (0.2-5.0%; n=2/141) and 1.4% (0.6-2.7%; n=8/576), respectively. In the one-week period following initial infections, no school-related secondary infections were detected, while the attack rate in households was 1.1% ([0.3-2.9]; n=4/352 persons with exposed index participant following the initial cross-sectional assessment.

    Study strengths

    Classrooms were selected at random, indicating that in expectation, there should be no characteristics of the classrooms that would make them have a different infection prevalence than other classrooms in Berlin. The use of both PCR and antibody testing on all individuals regardless of symptoms is an additional strength.

    Limitations

    These data were cross-sectional and represented a small window of time (less than a month); less can be said using these data on trends in transmission over time, and it is unclear whether what was captured here was representative of a larger period or not. The total number of events (cases) was small, making it difficult to describe differences by the use of different infection prevention and control measures.

    Value added

    This study provides a snapshot of potential transmission of SARS-CoV-2 in 24 classrooms and their associated households in Berlin, Germany.

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