[Low transmission of SARS-CoV-2 at school settings: a population-based study in the Basque Country.].

Objective: Studies about SARS-CoV-2 transmission at school settings have been outbreaks or schools clusters. There are scarce population-based studies has been studied. We aimed at describing SARS-CoV-2 school-related transmission and its relationship with baseline community cumulative incidence rate in the Basque Country after school reopening in order to inform Public Health decision-making.

Methods: We conducted a scholar surveillance population-based study of SARS-CoV-2 transmission from 7 September to 31 October 2020. We calculated percentages of cases in school-age population, secondary attack rates by education level among close contacts and correlation between population´s and scholars´ incidence rates at municipal level.

Results: There were 35,477 SARS-CoV-2 laboratory confirmed cases. Among them, 7.65% happened at school settings. Secondary attack rate at schools ranged from 2.9%, in preschools to 7.1% in high schools; Scholars caused a household and social secondary attack rate from 13% (high scholars) to 23.2% (elementary scholars). We found a low correlation between population´s and scholars´ incidence rates at municipal level (R2=0.047).

Conclusions: Secondary attack rate at school settings increased as educational level did; conversely, to social and family secondary attack rate, that decreased with higher educational level. School attendance, during a SARS-CoV-2 high transmission period showed feasible and did not rise transmission. These findings happened under strict non-pharmaceutical measures at school settings and proper epidemiological surveillance, including tracing of laboratory confirmed cases of SARS-CoV-2 looking for close contacts, isolation and testing of close contacts during isolation period. The different degree of transmission of the circulating variants in the different periods of the pandemic must also be taken into account.