Factors affecting the transmission of SARS-CoV-2 in school settings

Reynolds, C.; Ng, S.; Yang, W.

Background Several studies have reported SARS-CoV-2 outbreaks in schools, with a wide range of secondary attack rate (SAR; range: 0-100%). We aimed to examine the key risk factors to better understand transmission in school settings. Methods We collected records of SARS-CoV-2 school outbreaks globally published from January 2020 to January 2021 and compiled information on hypothesized risk factors. We utilized the directed acyclic graph (DAG) to conceptualize the risk mechanisms, used logistic regression to examine each risk-factor group, and further built multiple variable models based on the marginal analysis. Adjusted odds ratios (aOR) and 95% confidence intervals (CI) were calculated. Results From 17 relevant articles, 26 school clusters were included for analysis. The best-fit model showed that the intensity of community transmission (aOR: 1.26; 95% CI: 1.22 - 1.30, for each increase of 10 cases per 100,000 persons per week), social distancing (aOR: 0.26; 95% CI: 0.18 - 0.37), mask-wearing (aOR: 0.52; 95% CI: 0.35 - 0.78) were associated the risk of SARS-CoV-2 infection in schools. Compared to students in pre-schools, the aOR was 0.12 (95% CI: 0.07 - 0.19) for students in primary schools and 1.31 (95% CI: 0.93 - 1.87) for students in high schools. Conclusions Preventive measures in both schools (e.g. social distancing and mask-wearing) and communities (additionally, vaccination) should be taken to collectively reduce transmission and protect children in schools. Flexible reopening policies may be considered for different levels of schools given their risk differences.