Do cloth masks work?

Question. Do cloth masks work? With more states and localities issue mask mandates while in public and private businesses requiring them while in their store, their usage is growing. I myself use cloth masks when in a public space. But there’s always been a question about how effective they are. N95 masks filter out 95% of particles. What percentage do cloth masks filter? While I haven’t seen anything to give a definitive and specific number, I think there is a clear answer: enough to justify wearing them.

One laboratory experiment looked at how different facial coverings effected the distance respiratory droplets traveled compared to not wearing a mask.

Without a mask, droplets traveled more than 8 feet; with a bandana, they traveled 3 feet, 7 inches; with a folded cotton handkerchief, they traveled 1 foot, 3 inches; with the stitched quilting cotton mask, they traveled 2.5 inches; and with the cone-style mask, droplets traveled about 8 inches.  

Similarly, University of California, San Francisco professor of Medicine Monica Gandhi is expected to publish a literature review showing masks can also provide an important barrier for the person wearing them. That could lead to milder infections or even prevent them.

A second study looked at the outbreaks in Wuhan, China, Italy, and New York City to examine the impact of different mitigation measures. The study found:

Our analysis reveals that the difference with and without mandated face covering represents the determinant in shaping the pandemic trends in the three epicenters. This protective measure alone significantly reduced the number of infections, that is, by over 78,000 in Italy from April 6 to May 9 and over 66,000 in New York City from April 17 to May 9. Other mitigation measures, such as social distancing implemented in the United States, are insufficient by themselves in protecting the public. We conclude that wearing of face masks in public corresponds to the most effective means to prevent interhuman transmission, and this inexpensive practice, in conjunction with simultaneous social distancing, quarantine, and contact tracing, represents the most likely fighting opportunity to stop the COVID-19 pandemic.

A third study exploited variations created by mask mandates in 15 states too look at the impact of masks in daily COIVD-19 growth rates.

Mandating face mask use in public is associated with a decline in the daily COVID-19 growth rate by 0.9, 1.1, 1.4, 1.7, and 2.0 percentage-points in 1–5, 6–10, 11–15, 16–20, and 21+ days after signing, respectively. Estimates suggest as many as 230,000–450,000 COVID-19 cases possibly averted By May 22, 2020 by these mandates.

While the study is unable to differentiate the impact of cloth masks versus surgical masks or N95 respirators, I think it’s undebatable that cloth masks represent a large portion of the masks worn by people. This study, at a minimum, strongly suggests that cloth masks are effective.

We also have a powerful anecdote from Missouri. Two hair stylists saw 139 clients while unknowingly being infected with COVID-19. They both wore cloth masks and had their clients do the same. There is no evidence of any transmission.

The investigators found that none of the stylists’ 139 clients or secondary contacts became ill, and all 67 clients who volunteered to be tested showed no sign of infection.

Both stylists wore double-layered cloth face coverings or surgical masks when seeing clients. The median appointment time was 15 minutes and ranged from 15 to 45 minutes. More than 98% of clients wore a face covering—47% wore cloth face coverings, 46% wore surgical masks, and about 5% wore N-95 respirators.

So, cloth masks are clearly effective, but how common do they need to be to change the course of the pandemic? Below are two graphics illustrating the level of mask wearing and effectiveness in different scenarios needed to achieve different R0s.

Exit quote: “If we could get everybody to wear a mask right now, I think in four, six, eight weeks we could bring this epidemic under control.” – Robert Redfield, director of the Centers for Disease Control and Prevention

Update: Wanted to add additional evidence that I’ve come across since this article was published. First, a study from the University of North Texas. They found evidence that mask mandates had an effect on “daily new cases, emergency room visits and hospitalizations” that could be seen in both state level data and Texas county level data.

Second, a survey of 39 studies to determine the effectiveness of N95, surgical, and cloth masks for preventing respiratory virus infections. The analysis found that masks did help slow community spread and did not find evidence of health effects.

Lastly, a study found masks protected healthcare workers.

Update 2:

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