Little is known about how various interventions impact the spread of covid-19 in schools. Here, we examined effects of different types of rotations in various testing contexts using an agent-based modified SIER model run on real contact data acquired in an elementary school in Czechia (624 schoolchildren, 55 teachers, 27k social contacts). The results show that weekly rotations of in-class and distance learning reduce the spread of covid-19 by >75%; regular low-sensitivity (<40%) antigen testing twice a week significantly reduces infections; and the density of revealed contact graphs for older pupils is 1.5 times higher than the younger pupils graph, the teachers network is yet an order of magnitude denser. The results imply that teachers play a disproportionate role in spreading covid-19 and that weekly rotations with regular testing are an effective preventive intervention that can help to keep schools open during a worsened epidemic situation.

Purpose: It is unclear how much opening of schools during Covid-19 pandemic contributes to new SARS-CoV-2 infections among children. We investigated the impact of school opening with various mitigation measures (masks, rotations, mass testing) on growth rate of new cases in child cohorts ranging from kindergartens to upper secondary in Czechia, a country heavily hit by Covid-19, since April 2020 to June 2021. Methods: Our primary method is comparison of the reported infections in age cohorts corresponding to school grades undergoing different regimes. When there is no opportunity for such a comparison, we estimate corresponding coefficients from a regression model. In both the cases, we assume that district-level infections in particular cohorts depend on the school attendance and the external environment in dependence on the current overall risk contact reduction. Results: The estimates of in-cohort growth rates were significantly higher for normally opened schools compared to closed schools. When prevalence is comparable in the cohorts and general population, and no further measures are applied, the in-cohort growth reduction for closed kindergartens is 29% (SE=11%); primary: 19% (7%); lower secondary: 39% (6%); upper secondary: 47% (6%). For secondary education, mitigation measures reduce school-related growth 2-6 times. Conclusion: Considering more infectious SARS-CoV-2 variants and the 'long covid' risk, mitigation measures in schools, especially in secondary levels, should be implemented for the next school year. Some infections, however, are inevitable, even in kindergartens (where mitigation measures are difficult to implement) and primary schools (where they may not work due to low adherence).