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The Twelve Days of Mask Mess: Day 6

For the sixth day of mask mess, we got these:

Zhang et al.

Identifying airborne transmission as the dominant route for the spread of COVID-19. Proceedings of the National Academy of Sciences (2020), 117 (26) 14857-4863.

Published June 11, 2020, this study is very important to the Cooper administration. It was one of the studies Cooper listed among the five “examples of studies studying the effectiveness of face coverings” that he included in his Nov. 23 executive order tightening his mask order against people. It was also among the three studies presented before the General Assembly by state health bureaucrat Mandy Cohen on June 17, a week before Cooper first leveled his mask order on people (discussed here).

What the study purported to find was that mandated face masks were “the determinant in shaping the pandemic trends worldwide,” arguing that “wearing of face masks in public corresponds to the most effective means to prevent interhuman transmission.”

I explained how Zhang et al. arrived at that conclusion:

Italy didn’t mandate face masks until April 6 (northern Italy, then the rest of Italy on May 4), and NYC didn’t mandate face masks until April 17. Zhang et al. projected a linear (“no mask”) assumption in case increases in Italy and NYC, and then compared their projection with actual cases. The differences between actual cases and their linear (“no mask”) assumption are where they derived their finding quoted by Cohen: “Our analysis indicates that face coverings reduced the number of infections by over 78,000 in Italy from April 6 to May 9 and by over 66,000 in NYC from April 17 to May 9.” …

A major problem was, as I pointed out, both Italy and NYC were well past their case peaks when masks were mandated. Cases were falling already as a consequence of being on the other side of the infections spike:

Italy and NYC’s impositions of their mask mandates well after their peak of daily new cases makes it difficult to ascertain how much actual effect their mask mandates had on cases. Expecting a linear progression of cases post-peak also seems inflationary to the number of cases (under a no-mask assumption) over time.

Of note here: The original link for this study provided by the Cooper administration is broken. Searching for a proper link to the study yielded a scientific controversy — including a letter signed by 45 epidemiologists signed on to a letter making a formal request for retraction of the paper. They cited numerous methodological errors and “verifiably false” statements.

Does this study support Cooper’s extreme exercise of power?


This study is highly problematic. A study beset with so many methodological errors and “verifiably false” statements that 45 epidemiologists formally requested its retraction absolutely must not serve as a basis for an extreme emergency order.

Wang et al.

Reduction of secondary transmission of SARS-CoV-2 in households by face mask use, disinfection and social distancing: a cohort study in Beijing, China. BMJ Glob Health (2020).

Received May 1, 2020, this study is a retrospective cohort study of household transmission of COVID-19 by people with confirmed infections (“primary cases”). It relied on telephone interviews asking family members to self-reportmask-wearing, hygienic behaviors, physical distancing practices, close contact, living arrangements, room ventilation and cleaning, disinfectant use, separate eating utensils, etc. The primary cases had to have had fevers and a respiratory symptom, evidence of pneumonia, a normal to reduced white blood cell count, and a decreased lymphocyte count. They also must have either visited or lived in Wuhan, China, in the 14 days prior to symptoms, been in contact with someone who had, or been in a known cluster case.

Wang et al. conclude that:

This study reinforces the high risk of transmission in households but importantly shows that UFMU [universal face mask use] and hygiene measures can significantly reduce the risk of household transmission of COVID-19, independent of household size or crowding. This is the first study to show the effectiveness of precautionary mask use, social distancing and regular disinfection in the household, and can inform guidelines for prevention of household transmission.

Wang et al. found that in households with a proven case, “Face masks were 79% effective and disinfection was 77% effective, while close frequent contact in the household increased the risk of transmission 18 times, and diarrhoea in the index patient increased the risk by four times.” According to their introduction, “Community mask wearing, hand washing and social distancing are thought to be effective” — i.e., those communitywide effects were not being tested here — “but there is little evidence to inform or support community members on COVID-19 risk reduction within families.” They said their new findings “imply” support for masks and social distancing “inside the household with members at risk of getting infected.”

Nevertheless, Wang et al. realized that since “compliance of [universal mask use] would be poor in the home, there was difficulty and also no necessity for everyone to wear masks at home.” They narrowed their recommendations to those families with members “at risk of getting infected.”

Does this study support Cooper’s extreme exercise of power?


This study focuses on mask wearing, social distancing, hand washing, and disinfection in the household setting. It cannot be used for Cooper’s extreme emergency orders affecting people statewide.

Also, this study relies on telephone interviews asking people to remember things after the fact. It will be affected by all kinds of biases and confounders that researchers cannot help, including recall bias, observer bias, information bias, etc. It’s not a randomized controlled trial (RCT), which is the gold standard. Studies like these are unlikely to provide evidence compelling enough for extreme emergency orders.

Even where Cooper’s mask order affects people inside their own homes, it is not supported by this study. Wang et al. recommend — not call for government orders for — mask-wearing at home only for “those families with members who were at risk of getting infected,” such as “ever having contact with a COVID-19 patient, medical workers caring for a COVID-19 patient or having a history of travelling to high risk areas).” Cooper’s order assumes everyone is a risk to others by virtue of simply breathing. Such an assumption is insufficient for extreme emergency orders.

Click for more of the Twelve Days of Mask Mess series. 

Jon Sanders / Director of Regulatory Studies

Jon Sanders studies regulatory policy, a veritable kudzu of invasive government and unintended consequences. As director of regulatory studies at the John Locke Foundation, Jo...

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