The spread of SARS-CoV-2 at school through the different pandemic waves: a population-based study in Italy

Proactive school closures are often considered an effective strategy by policy-makers and the public to limit SARS-CoV-2 transmission. While evidence on the role of students in the spread is debated, the effects of closures on children's well-being are well known. In the light of this, we aimed to assess viral spread in educational settings, by calculating the rate of secondary infections per school class and identifying factors associated with cluster generation. We conducted a combined longitudinal and cross-sectional population-based study between October 2020 and November 2021. Secondary screening was conducted whenever a SARS-CoV-2 positive subject had been in the school environment in 48 h prior to symptoms onset or on the date of swab, if asymptomatic. The effect of selected variables on COVID-19 cluster generation was assessed by logistic regression. We identified 1623 primary COVID-19 cases. Of these, 72.5% resulted in no secondary case, 15.6% in 1, and 11.9% in 2 + . The probability of generating a 2 + cluster was lower when the index case was a student, rather than school staff (AOR = 0.42; 95%CI: 0.29-0.60). The number of clusters per week was in line with COVID-19 incidence trend in the general population.

Index cases at school led to no secondary case in about three out of four times and only to a secondary case in about 15%. School environment does not facilitate viral spread, but rather reflects circulation in the community. Appropriate measures and timely monitoring of cases make school a safe place. Given the effects on children's learning and well-being, it is essential to favour school attendance over distance learning.

• During the COVID-19 pandemic, most European countries resorted to school closures to counter viral transmission. • Although the scientific debate on the suitability of school closures as a non-pharmaceutical intervention is still open and the role of school children in facilitating the spread of SARS-CoV-2 is not supported by unequivocal evidence, there is now a growing awareness of the impact on children's well-being.

• The contribution of educational settings and students in facilitating viral spread appears limited, as exposure to a positive individual in the school environment led to no secondary cases among students in 72% of cases and only one secondary case in about 15%. • The likelihood of generating school clusters was approximately halved when the index case was a student compared to teachers or other school personnel.