A study estimating and comparing the transmission of airborne respiratory infections with and without air cleaners in schools. Air cleaners were installed in the classrooms of two classes in a secondary school in the Canton of Solothurn, Switzerland, between January 16 and March 11, 2023. The following data were collected - **Molecular data:** Bioaerosol and human saliva samples. - **Environmental data:** Carbon dioxide levels, aerosol and particle concentrations. - **Epidemiological data:** Daily absences from school. Laboratory and molecular analysis is performed to detect which respiratory infections (e.g. SARS-CoV-2 or Influenza virus) were spreading over the study. Molecular data (positive samples), environmental (particle concentrations), and epidemiological data (absences related to respiratory infections) are compared between study conditions with and without air cleaners. The aim of the comparison is to assess whether air cleaners reduced the risk of airborne infection.