HEPA Air Purifiers Show Limited Effectiveness in Reducing Viruses in Classrooms

Recent research indicates that relying solely on high-efficiency particulate air (HEPA) purifiers may not be sufficient to lower airborne viral exposure in school environments. The study, conducted by researchers from Mass General Brigham in collaboration with other institutions, analyzed the presence and diversity of respiratory viruses in elementary school classrooms equipped with HEPA air purifiers compared to those without effective filtration.

The investigation was a secondary analysis of a previously conducted randomized clinical trial, which originally aimed to determine whether HEPA purifiers could alleviate asthma symptoms among students. The study encompassed 200 classrooms in public elementary schools located in the Northeastern United States, with participants being students diagnosed with asthma. Classrooms were randomly assigned either functional HEPA purifiers or placebo devices lacking filtration capacity.

Researchers assessed air samples from classrooms for the presence of 19 different respiratory viruses, including common and potentially serious pathogens such as respiratory syncytial virus (RSV) and influenza. The results revealed that viruses were present in nearly all (98.4%) of the air samples collected. On average, each classroom sample contained three distinct types of viruses, with certain classrooms registering up to 13 different viral types.

The findings showed that HEPA purifiers did not lead to a significant reduction in the overall concentration of airborne respiratory viruses. While a modest decrease of approximately 32.8 percent in viral diversity was observed in classrooms with HEPA filtration, this reduction did not translate into fewer school absences among students. This suggests that, although HEPA purifiers may slightly limit the variety of viruses circulating in the air, they are not sufficient as a standalone measure to lower the risk of viral transmission in school settings.

Additionally, the study identified an association between low indoor humidity levels and increased viral presence in classroom air. The data indicated that maintaining indoor humidity within the range of 40% to 60% could play a role in decreasing the prevalence of certain airborne viruses. This points to humidity control as a potential complementary strategy for improving indoor air quality and reducing viral exposure, alongside air filtration and enhanced ventilation.

The study highlights the complex nature of airborne viral transmission in schools and the need for multifaceted approaches to protect the health of students and staff. While HEPA air purifiers can contribute to improving air quality by reducing particulate matter, their limited impact on viral load underscores the importance of combining multiple interventions. These may include maintaining optimal humidity levels, increasing ventilation, and implementing other infection control measures.

Experts suggest that future efforts to minimize viral exposure in educational facilities should consider a comprehensive strategy that integrates air purification, humidity regulation, and ventilation improvements. Such an approach could offer better protection against the spread of respiratory viruses, helping to safeguard both student wellbeing and consistent school attendance.

For more detailed information, the full study is available in JAMA Network Open, providing valuable insights into the effectiveness of air purification technologies in real-world classroom settings and guiding public health policies for schools.