HEPA purifiers alone may not be enough to reduce viral exposure in schools

The issue of viral illness spreading in schools has become a major concern as students return to in-person learning. A recent study conducted by researchers from Mass General Brigham has shed light on the effectiveness of high-efficiency particulate air (HEPA) purifiers in reducing exposure to respiratory viruses in classrooms.

The study, published in JAMA Network Open, revealed that even with the presence of HEPA purifiers in classrooms, the exposure to respiratory viruses remained high. Air samples collected from classrooms showed an average of three different respiratory viruses per room, with some classrooms containing as many as 13 different viruses, including pathogens like respiratory syncytial virus (RSV) and influenza virus.

Dr. Peggy S. Lai, the corresponding author of the study, emphasized that the use of HEPA purifiers did not significantly reduce the overall viral load in classrooms. This suggests that additional interventions may be necessary to effectively mitigate the spread of respiratory viruses in school settings.

HEPA filters are designed to filter out fine particulate matter from the air, but their effectiveness in filtering respiratory viruses transmitted through aerosols and droplets has been limited. The researchers conducted a secondary analysis of the School Inner-City Asthma Intervention Study (SICAS-2), which originally aimed to assess the impact of HEPA purifiers on asthma symptoms in elementary school students.

While the study did show a modest decrease in viral diversity in classrooms with HEPA purifiers, this reduction was not associated with a decrease in school absences. The researchers also noted a correlation between lower humidity levels and higher viral exposure, suggesting that maintaining optimal humidity levels in classrooms may play a crucial role in lowering viral exposures.

Dr. Lai highlighted the importance of implementing comprehensive strategies to reduce the risk of respiratory virus transmission in schools. In addition to air filtration and ventilation improvements, maintaining humidity levels between 40% and 60% could be a key factor in reducing viral exposures and enhancing the overall comfort and safety of students and teachers.

The findings from this study underscore the complexity of addressing viral transmission in educational settings and emphasize the need for multifaceted approaches to mitigate the risk of respiratory illnesses among school-aged children and educators. Further research and interventions are warranted to develop effective strategies for creating safer and healthier learning environments.