Analysis Finds that Universal Masking Reduces Classroom Transmission by 800%

A new study published in BMJ last week called SARS-CoV-2 aerosol transmission in schools: the effectiveness of different interventions found that universal masking in classrooms reduced aerosol transmission by 800%. Ventilation “… through the full opening of six windows all day during the winter reduces transmission by 14x“.

The combined interventions of universal masking, natural ventilation, and HEPA filtration) reduced transmission 3,000%. Sadly, we have a governor that is actually paying schools extra money to ignore CDC recommendations on universal masking knowing full well that his policy is jeopardizing student’s health and safety.

Results: 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).

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.


New Evidence: 33% of COVID-19 Infections are Asymptomatic: Results Support School Testing/Masking/Ventilation

Asymptomatic SARS-CoV-2 infection: A systematic review and meta-analysis | PNAS

By analyzing over 350 papers in this systematic review, the researchers found that more than one-third of infections are truly asymptomatic. The review found more asymptomatic infections among kids and fewer among older folks and people with underlying health conditions.

These results suggests that heightened vigilance is needed in schools (e.g. masking and testing) to prevent spillover into the broader community.


Outbreak Associated with SARS-CoV-2 B.1.617.2 (Delta) Variant in an Elementary School | MMWR (

Conclusion: Vaccines are effective against the Delta variant, but transmission risk remains elevated among unvaccinated persons in schools. In addition to vaccination, strict adherence to multiple nonpharmaceutical prevention strategies, including masking, are important to ensure safe school instruction.

Governor Ducey will have absolutely no interest in these new findings, as the results don’t support his pre-existing belligerence toward mitigation measures in schools.

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