HEPA Purifiers Do Not Reduce Viral Exposures in Classrooms

TUESDAY, Oct. 21, 2025 (HealthDay News) — High-efficiency particulate air (HEPA) purifiers are not associated with a reduction in high viral exposure in elementary school classrooms, according to a study published online Oct. 10 in JAMA Network Open.

Ye Sun, M.D., from Boston Children’s Hospital, and colleagues examined whether HEPA purifiers are associated with reduced respiratory virus exposure in elementary school classrooms. The analysis included 532 bioaerosol samples from 200 classrooms randomly assigned to receive either active HEPA purifiers or visually identical sham HEPA units (four per classroom).

The researchers found that viruses were detected in 98.5 percent, with a median of three viruses per classroom, including most commonly rhinovirus (89.5 percent), respiratory syncytial virus A and B (12.4 and 23.9 percent, respectively), and influenza A and B (17.7 and 14.3 percent, respectively). High viral exposure was present in 22.2 percent of samples. There was no association between the HEPA purifier intervention and lower odds of high viral exposure (odds ratio [OR], 0.50; 95 percent confidence interval [CI], 0.08 to 3.25; P = 0.46), but it did correspond to a modest reduction in viral diversity (β = −1.02; 95 percent CI, –1.68 to −0.35; P = 0.003). Relative humidity, grade, winter season, and coarse particulate matter were the environmental risk factors tied to viral exposure.

“In addition to air filtration or better ventilation, maintaining classroom humidity between 40 and 60 percent may help lower viral exposures and improve comfort for students and teachers,” coauthor Peggy S. Lai, M.D., from Massachusetts General Hospital in Boston, said in a statement.

One author disclosed ties to the pharmaceutical industry.

Abstract/Full Text