Installing HEPA air purifiers in classrooms may not significantly reduce students’ exposure to respiratory viruses, according to new research in America.
In a secondary analysis of data from 200 U.S. classrooms, researchers found that even rooms equipped with high-efficiency particulate air (HEPA) purifiers still had high levels of airborne respiratory viruses.
The findings suggest that while HEPA filters can remove dust and fine particles, they may be less effective at capturing viruses spread through aerosols and droplets and that additional measures may be needed to make classrooms safer.
The study analysed data from the School Inner-City Asthma Intervention Study (SICAS-2), which followed elementary school students with asthma between 2015 and 2020. Classrooms were randomly assigned to receive either portable HEPA purifiers or devices without filters. Researchers then examined air samples for the presence of 19 common respiratory viruses.
It was found that 98% of air samples contained viral material, and classrooms averaged three different respiratory viruses per room, with some detecting as many as 13, including influenza and respiratory syncytial virus (RSV).
Dr Peggy S. Lai, physician-scientist at Mass General Brigham said: ‘Air purifiers did not reduce overall viral load in classrooms, suggesting that additional interventions may be needed in schools.’
While the HEPA-equipped classrooms showed a 32% reduction in viral diversity, this didn’t translate to fewer school absences or lower viral exposure overall. The researchers also found that low humidity was linked to higher viral concentrations, suggesting that humidity control could play an important role in reducing airborne transmission.
The findings highlight the complexity of managing air quality in schools and the need for layered strategies — combining ventilation, humidity control, and public health measures — to help curb the spread of infections.
Lai added: ‘School-aged children and teachers face increased risks from respiratory viruses, which can impact their health, lead to missed school days, and create challenges for families.
‘While our study did not find that HEPA air purifiers reduced high viral exposure in classrooms, it’s important to note that the trial was originally designed to measure other outcomes. In addition to air filtration or better ventilation, maintaining classroom humidity between 40% and 60% may help lower viral exposures and improve comfort for students and teachers.’
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