mask science {part 1}

Mask-free paperwork to hand managers of public accommodation:

Wearing a mask is hazardous to your health:


Effectiveness of masks at preventing           transmission of respiratory pathogens:

1 — T Jefferson, M Jones, et al. Physical interventions to interrupt or reduce the spread of respiratory viruses. MedRxiv. 2020 Apr 7.

Meta-analysis – face masks were found to have no detectable effect against transmission of viral  infections. “Compared to no masks, there was no reduction of influenza-like illness cases or influenza for masks in the general population, nor in healthcare workers.”


2 — J Xiao, E Shiu, et al. Nonpharmaceutical measures for pandemic influenza in non-healthcare settings – personal protective and environmental measures. Centers for Disease Control. 26(5); 2020 May.

Meta-analysis – evidence from randomised controlled trials of face masks did not support a substantial effect on transmission of laboratory-confirmed influenza, either when worn by infected persons (source control) or by persons in the general community to reduce their susceptibility.


3 — J Brainard, N Jones, et al. Facemasks and similar barriers to prevent respiratory illness such as COVID19: A rapid systematic review. MedRxiv. 2020 Apr 1.

Systematic review: masks had no effect specifically against Covid-19, although facemask use seemed linked to 3 in 31 of studies “very slightly reduced” odds of developing influenza-like illness.”


4 — L Radonovich M Simberkoff, et al. N95 respirators vs medical masks for preventing influenza among health care personnel: a randomized clinic trial. JAMA. 2019 Sep 3. 322(9): 824-833.

Randomized clinical trial – 2019 – 2862 participants showed that both N95 respirators and surgical masks “resulted in no significant difference in the incidence of laboratory confirmed influenza.”


5 — J Smith, C MacDougall. CMAJ. 2016 May 17. 188(8); 567-574.

Meta-analysis – both randomized controlled trials and observational studies of N95 respirators and surgical masks used by healthcare workers did not show benefit against transmission of acute respiratory infections. Acute respiratory transmission “may have occurred via contamination of provided respiratory protective equipment during storage and reuse of masks and respirators throughout the workday.”


6 — F bin-Reza, V Lopez, et al. The use of masks and respirators to prevent transmission of influenza: a systematic review of the scientific evidence. 2012 Jul; 6(4): 257-267.

Meta-analysis – 17 studies regarding masks and effect on transmission of influenza found that “none of the studies established a conclusive relationship between mask/respirator use and protection against influenza action.” However, authors speculated that effectiveness of masks may be linked to early, consistent and correct usage.


7 — J Jacobs, S Ohde, et al. Use of surgical face masks to reduce the incidence of the common cold among health care workers in Japan: a randomized controlled trial. Am J Infect Control. 2009 Jun; 37(5): 417-419.

Randomised controlled trial – face mask use was found to not be protective against the common cold, compared to controls without face masks among healthcare workers.

Airflow around masks:

8 — M Viola, B Peterson, et al. Face coverings, aerosol dispersion and mitigation of virus transmission risk.

Original article – asks assumed to be effective in obstructing forward travel of viral particles. Those positioned next to or behind a mask wearer received farther transmission of virus-laden fluid particles from masked individuals than from unmasked individuals by means of “several leakage jets, including intense backward and downwards jets that may present major hazards,” and a “potentially dangerous leakage jet of up to several metres.” All masks were thought to reduce forward airflow by 90% or more over wearing no

mask. However Schlieren imaging showed that both surgical masks and cloth masks had farther brow jets (unfiltered upward airflow past eyebrows) than not wearing any mask at all, 182mm and 203mm respectively vs none discernible with no mask. Backward unfiltered airflow was found to be strong with all masks compared to not masking.


9 S Grinshpun, H Haruta, et al. Performance of an N95 filtering facepiece particular respirator and a surgical mask during human breathing: two pathways for particle penetration. J Occup Env Hygiene. 2009; 6(10):593-603.

Original article – both N95 and surgical masks, it was found that expelled particles from 0.03 to 1 micron were deflected around the edge of each mask, and that there was measurable penetration of particles through the filter of each mask.


Penetration through masks:

10 — H Jung, J Kim, et al. Comparison of filtration efficiency and pressure drop in anti-yellow sand masks, quarantine masks, medical masks, general masks, and handkerchiefs. Aerosol Air Qual Res. 2013 Jun. 14:991-1002.

Original study – study of 44 mask brands found mean 35.6% penetration (+34.7%). Most medical masks had over 20% penetration while “general masks and handkerchiefs had no protective function in terms of the aerosol filtration efficiency.” Findings – “medical masks, general masks and handkerchiefs were found to provide little protection against respiratory aerosols.”


11 — C MacIntyre, H Seale, et al. A cluster randomized trial of cloth masks compared with medical masks in healthcare workers. BMJ Open. 2015; 5(4)

Randomised control trial – penetration of cloth masks by particles was almost 97% and medical masks 44%.


mask science {part 2}
mask science {part 3}

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