Classroom air purifiers for reducing school absence: study protocol for a pragmatic, cluster-randomised, parallel,
Runar B Solberg1, Sverre B Holøs2, Ingeborg Hess Elgersma3
1Centre for Epidemic Interventions Research, Norwegian Institute of Public Health, Oslo, Norway runar.solberg@fhi.no.
BMJ Open
|December 25, 2025
Summary
This study investigates if High Efficiency Particulate Air (HEPA) filter air purifiers reduce student absenteeism in primary schools. Findings will inform non-disruptive strategies for managing respiratory infections in classrooms.
Area of Science:
- Public Health
- Epidemiology
- Environmental Health
Background:
- Respiratory infections pose significant global health risks, with schools identified as high-transmission settings.
- COVID-19 school closures disrupted education and well-being, highlighting the need for non-disruptive mitigation strategies.
- Evidence for the effectiveness of High Efficiency Particulate Air (HEPA) filter air purifiers in reducing viral transmission in schools is limited.
Purpose of the Study:
- To estimate the effect of portable HEPA air purifiers on student absenteeism in primary school classrooms.
- To assess the impact of HEPA air purifiers on teacher absenteeism and respiratory infection rates.
- To evaluate the cost-effectiveness and implementation of air purifiers in educational settings.
Main Methods:
- A cluster-randomised, parallel, two-arm, group sequential superiority trial involving primary schools in Norway.
- Randomisation of schools to receive either HEPA air purifiers or sham air purifiers.
- Primary outcome: student absenteeism measured as aggregated full child days of absence at the class level, with an interim analysis for early stopping.
Main Results:
- The study is designed to determine if HEPA air purifiers significantly reduce student absenteeism compared to sham purifiers.
- Secondary outcomes include reductions in teacher absenteeism and self-reported respiratory infections.
- A cost-consequence analysis will be performed if a statistically significant effect on the primary outcome is observed.
Conclusions:
- This trial will provide crucial evidence on the efficacy of HEPA air purifiers as a non-disruptive intervention to mitigate respiratory infections in schools.
- Findings will inform public health policies and school management strategies for improving indoor air quality and reducing school-related illness.
- The study aims to offer practical solutions for maintaining educational continuity during respiratory virus seasons.
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