Introduction
Different public health measures were implemented during the COVID-19
pandemic to maintain the schools open1,2. Regarding
COVID-19 vaccination, at the beginning of this study, more than 92% and
40% of population older than 12 years and children aged 5-11 years in
Spain was fully vaccinated against COVID-19,
respectively3.
Ventilation was proposed as one of the main strategies to reduce aerosol
transmission for SARS-CoV-2 during the pandemic. A study from Germany
assessed the efficiency of air purifiers in reducing aerosols in
high-school classrooms4. However, no clinical
endpoints were investigated and, therefore, a very low certainty of
evidence was graded by a Cochrane review5. In an
Italian study, the authors concluded that ventilation reduced the
likelihood of SARS-CoV-2 infection in classrooms by
80%6. Moreover, a survey study from the US reported
that elementary schools with face masks and ventilation strategies in
place had lower SARS-CoV-2 incidence rates7. In a
Lancet Task Force Commission review8, the authors
concluded that improving building ventilation systems may carry benefits
beyond protection from COVID-19. However, there is scarce evidence that
demonstrate the association of epidemiological and environmental risk
factors, including CO2 concentrations, with the
incidence of respiratory tract infections (RTI) in children who are
attending schools.
The present study is part of COVID-19 Sentinel Schools Network of
Catalonia (CSSNC), a project including 23 schools and 5687 students,
teachers and other school staff with the aim to monitor SARS-CoV-2 and
other respiratory viruses, their determinants and preventive measures in
Catalonia9. The objectives of this study are to assess
the potential association of demographic and epidemiological factors,
including the indoor environmental conditions (CO2levels) in the classrooms, with students’ school absence due to RTI.