Yesterday I gave a talk for the Arizona Association of School Business Officials about COVID. During the talk I discussed a few evidence-based interventions that lower transmission of COVID in schools, including universal masking, ventilation and air filtration. After the talk, a few of the attendees asked me for the study I was referencing during my talk called SARS-CoV-2 aerosol transmission in schools: the effectiveness of different interventions.

I thought I’d post this blog so everybody could find that study easier. Here are the Results and Conclusions of the study:


The most effective single intervention was natural ventilation through the full opening of six windows all day during the winter (14-fold decrease in cumulative dose), followed by the universal use of surgical face masks (8-fold decrease). In the spring/summer, natural ventilation was only effective (≥ 2-fold decrease) when windows were fully open all day. In the winter, partly opening two windows all day or fully opening six windows at the end of each class was effective as well (≥ 2-fold decrease).

One HEPA filter was as effective as two windows partly open all day during the winter (2.5-fold decrease) while two filters were more effective (4-fold decrease). Combined interventions (i.e., natural ventilation, masks, and HEPA filtration) were the most effective (≥ 30-fold decrease). Combined interventions remained highly effective in the presence of a super-spreader.


Natural ventilation, face masks, and HEPA filtration are effective interventions to reduce SARS-CoV-2 aerosol transmission. These measures should be combined and complemented by additional interventions (e.g., physical distancing, hygiene, testing, contact tracing, and vaccination) to maximize benefit.