Face Masks – A Summary of Relevant Research Papers for COVID-19

11 Jun

Below are papers published in the last couple months or so related to face mask use and their effectiveness for reducing SARS-CoV-2 transmission. For each paper I list the following:

  • Title
  • Publish Date
  • Source (what journal is it from)
  • What it says (a brief summary)

I want to state at the start that, while I do work in an area of public health, I am not an epidemiologist. I have a background in chemistry (undergrad) and biological sciences (graduate). I’m not claiming at all to be an expert in COVID-19 and face masks. That’s why I read the peer reviewed papers from those that are. I am, however, qualified enough to write these annotations about the papers, which I’ve done, but I’ve also provided links to each study and I’d encourage you to read them for yourself for more information beyond my summary. (Note that a couple of the annotations were taken from a post written by Dr. Jennifer Kasten. She is a medical doctor and a pathologist, with degrees in infectious disease epidemiology and mathematical modeling of epidemics, and fieldwork in epidemic control. When I used her comments, I include her name after the “what it says”. You can find the source of her comments here.)

These links and the information are here for your use to share. I will try to update as appropriate. Feel free to link to this page or just take the whole thing and copy and paste it somewhere else. I don’t need any credit for it. Please just get the info out so we can slow this thing. (Last updated 07/27/2020.)

Since April 3rd, the CDC has advocated for the use of masks in public largely to reduce the spread of asymptomatic and pre-symptomatic transmission. Many academic papers and articles have been published in the last couple months on the issue, and almost universally, they advocate for the benefits of wearing a mask. Below are many of them in the order of publish date. If you feel there’s a key one I’m missing, please comment and I’ll try to include it.

(A quick note about older papers some people have shared to argue against mask use. First, many of those studies involved other viruses, usually influenza, with dramatically different transmission rates, and so they have limited application to SARS-CoV-2. Second, those studies generally offer little significance to the question of general public mask use because they are looking at reducing transmission TO healthcare workers, not FROM asymptomatic or pre-symptomatic persons, which is the primary purpose of wearing a mask in the current situation. Finally, some of the things being shared are simply false. I have put some info on that here and here, including a response to the widely circulated Rancourt article, and here, a recent Laura Ingraham segment.)

Current relevant papers

Title: Potential utilities of mask‐wearing and instant hand hygiene for fighting SARS‐CoV‐2
Publish Date: March 31, 2020
Source: Journal of Medical Virology
What it says: This research demonstrated that home made masks could block over 95% of virus in aerosols (and surgical masks over 97%).

Title: Respiratory virus shedding in exhaled breath and efficacy of face masks
Publish Date: April 3, 2020
Source: Nature Medicine
What it says (Kasten): Hong Kong study showed masking was very effective at reducing transmission of alpha coronaviruses.

Title: Effectiveness of Surgical and Cotton Masks in Blocking SARS–CoV-2: A Controlled Comparison in 4 Patients
Publish Date: April 6, 2020
Source: Annals of Internal Medicine
What it says: The statistical power of this study was weak, as it only had an “n” of 4. The authors initially concluded in the paper that “both surgical and cotton masks seem to be ineffective in preventing the dissemination of SARS–CoV-2 from the coughs of patients with COVID-19 to the environment and external mask surface.” Besides an n of 4, another issue with this study was that it only measured coughing, not asymptomatic or pre-symptomatic carrier speech, which is thought to be a key reason for wearing a mask. But alas, none of that matters as on June 1, this paper was retracted because the authors admitted to making a mistake by failing to accurately recognize the limits of the detection in the test they used. So the study is bunk.

Title: Visualizing Speech-Generated Oral Fluid Droplets with Laser Light Scattering
Publish Date: April 15, 2020
Source: New England Journal of Medicine
What it says: This is a brief report on a test using laser light to demonstrate the difference of speech-generated droplets and their trajectories when wearing a mask verses not wearing a mask. It clearly shows the benefits of wearing a mask in reducing droplet related transmission. Here is a video they produced. Please take the two minutes to watch it.

Title: To mask or not to mask: Modeling the potential for face mask use by the general public to curtail the COVID-19 pandemic
Publish Date: April 21, 2020
Source: Infectious Disease Modelling
What it says (Kasten): a mathematical model for COVID in New York and Washington shows: a) if 80% of people wear cloth masks which are 20% effective, mortality is reduced by up to 65% in low-prevalence Washington. B ) In high-prevalence New York, wearing 50% effective masks reduces mortality by up to 45%.

Title: Cloth Masks May Prevent Transmission of COVID-19: An Evidence-Based, Risk-Based Approach
Publish Date: May 22, 2020
Source: Annals of Internal Medicine
What it says:  This report from an international research team made up of a number of MD’s and other specialists, reviews the data available on cloth masks and concludes that cloth masks worn by the public will reduce COVID-19 transmission rates, and furthermore, those benefits outweigh any risks that may be brought about by wearing masks (such as improper use).

Title: Reducing transmission of SARS-CoV-2
Publish Date: May 27, 2020
Source: Science
What it says: This paper authored by aerosol chemists and an infectious disease specialist argues that masks are necessary. The team analyzed both analytical information about the virus and looked at countries where masks are commonplace. They note “airborne spread from undiagnosed infections will continuously undermine the effectiveness of even the most vigorous testing, tracing and social distancing programs.”

Title: Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis
Publish Date: June 1, 2020
Source: Lancet
What it says: A review of 172 observational studies and 44 relevant comparative studies. The authors summarize their findings and regarding the use of face masks conclude, “Face mask use could result in a large reduction in risk of infection.” They note that N95 respirators or similar would likely result in added benefits.

Title: A modelling framework to assess the likely effectiveness of facemasks in combination with ‘lock-down’ in managing the COVID-19 pandemic
Publish Date: June 10, 2020
Source: Proceedings of the Royal Society A
What it says: The authors advocate for widespread use of face masks to keep the R0 below 1.0. They conclude, “facemask adoption by entire populations would have a significant impact on reducing COVID-19 spread” and “in summary, our modelling analyses provide support for the immediate, universal adoption of facemasks by the public”.

Title: Identifying airborne transmission as the dominant route for the spread of COVID-19
Publish Date: June 11, 2020
Source: PNAS
What it says: This study is a retrospective observational look at three epicenters of COVID-19 outbreak (Wuhan, Italy and New York), examining mask use, including after effects of mandatory implementation (in Italy and New York). Based on their analysis, they conclude that mask use is “the most effective means to prevent interhuman transmission”.
IMPORTANT NOTE: The methodology in this paper has been called in to question by some epidemiologists, including one who has called for a retraction, but others are standing by its conclusions. UPDATE 6/19: A larger group of epidemiologists is now calling for a retraction. They write, “While masks are almost certainly an effective public health measure for preventing and slowing the spread of SARS-CoV-2, the claims presented in this study are dangerously misleading and lack any basis in evidence.” More to come.

Title: Face Masks Considerably Reduce COVID-19 Cases in Germany: A Synthetic Control Method Approach
Publish Date: June, 2020
Source: IZA
What is says: Using the synthetic control method to examine the impact of face masks, the authors analyzed COVID cases in different regions in Germany. For example, in Jena, the first German city to make face masks mandatory, the COVID-19 cases fell by almost 25%, 20 days after implementation. They conclude that the public use of face masks reduces the daily growth rate of COVID-19 by about 40%. This is substantial and would have a dramatic impact on the R0. They do note in their conclusion that different norms and climatic conditions in other countries might not result in the same level of protective outcomes as seen in Germany.

Title: On Respiratory Droplets and Face Masks
Publish Date: June 16, 2020
Source: Physics of Fluids
What it says: This study reviews droplet transmission through and around filters as a result of coughing. The conclusions reinforce other studies that have noted that workers in a healthcare environment should also be using face shields and other PPE. The relevance of this study to public face mask use is limited, except to serve as a reminder that face masks, while they reduce droplet transmission significantly, do not provide complete prevention of droplets when individuals cough. So, other measures such as social distancing and staying home when you are sick remain essential to mitigating COVID-19.

Title: Community Use of Face Masks and COVID-19: Evidence from a Natural Experiment of State Mandates in the US
Publish Date: June 16, 2020
Source: Health Affairs
What it says: This study looks back at the time period in the US from April 8 to May 15 and examines the effects of different governmental orders to wear face masks on COVID-19 growth rates. The authors suggest that the mandates which where in place prevented between 230,000 and 450,000 cases by May 22 (a reduction of 14-27%). There are some limitations to this research. For example, there is no way to measure compliance in different regions, and there were some city and county ordinances not accounted for. Still, this retrospective analysis (essentially a natural experiment) provides complementary evidence on the benefits of public use of face masks, along with other mitigation efforts.

Title: The Use of Facemasks May Not Lead to an Increase in Hand-face Contact
Publish Date: June 28, 2020
Source: Transboundary and Emerging Diseases
What it says: This study looked at video of bus passengers before and after COVID-19 to compare the amount of times people wearing masks verses not wearing masks touched their faces. The purpose was to determine if mask wearing indeed causes people to touch their face more, as has been advocated by some opponents of mask wearing. The researchers found that facial touching was essentially equal, if wearing a mask or not. Importantly though, they note that wearing a mask, “did reduce the risk of direct contact of the hands with the nose and mouth; a high-risk action for virus transmission.”

Title: Fundamental Protective Mechanisms of Face Masks Against Droplet Infections
Publish Date: June 28, 2020
Source: Journal of Aerosol Science
What it says: This paper looks at both transmission TO and transmission FROM. On the TO side (self-protection), they note that a surgical mask (or similar) likely will not provide sufficient protection for the wearer to protect against droplet infection (and only properly fitted particle-filtering masks, such as an N95, can offer that type of protection). On the FROM side, they note that a simple mouth and nose cover is effective at limiting droplet emission when breathing, speaking, singing, coughing or sneezing. A face covering greatly reduces the spread of virus. Thus, public wearing of face masks is, “a very useful contribution to contain a pandemic.”

Title: Visualizing the Effectiveness of Face Masks in Obstructing Respiratory Jets
Publish Date: June 30, 2020
Source: Physics of Fluids
What it says: This study shows how different types of home made cloth masks impact respiratory droplet travel. They tested different types of cloth made masks against emulated coughs and sneezes. All worked to varying degrees. They note that issues like leakage happen when improperly worn, but that nevertheless, home made cloth masks significantly reduce the distance traveled by expelled particles, and that they are especially effective in stopping larger respiratory droplets, which constitute the majority of total volume of ejected respiratory fluid.

Title: Association Between Universal Masking in a Health Care System and SARS-CoV-2 Positivity Among Health Care Workers
Publish Date: July 14, 2020
Source: JAMA
What it says: This study presents evidence that universal masking of health care workers and patients helps reduce transmission of SARS-CoV-2. The study presents data that shows after universal masking policies were put in place, cases of COVID-19 declined.

Title: Absence of Apparent Transmission of SARS-CoV-2 from Two Stylists After Exposure at a Hair Salon with a Universal Face Covering Policy — Springfield, Missouri, May 2020
Publish Date: July 14, 2020
Source: Morbidity and Mortality Weekly Report (MMWR)
What it says: 139 clients were exposed to two hair stylists with confirmed COVID-19. Both the stylists and the clients wore face masks. No evidence of transmission was reported. 67 clients were tested for SARS-CoV-2 and all test results were negative.

Title: Face coverings and mask to minimise droplet dispersion and aerosolisation: a video case study
Publish Date: July 24, 2020
Source: Thorax
What it says: The authors tested one-, two- and three-layer masks with speaking, coughing and sneezing. They found that all worked to block droplets, but that two-layer worked significantly better for coughs and sneezes. Three-layer surgical masks performed best. The authors suggest that guides for home-made masks should stipulate the use of a minimum of three-layers.

Below are papers still in the peer review process that I will likely include once completed. If you don’t have a background in the material, I would advise waiting for the peer review process, but I include them here as a reference for those in the fields.

Title: Assessment of Fabric Masks as Alternatives to Standard Surgical Masks in Terms of Particle Filtration Efficiency 

Title: Estimating the Effect and Cost-Effectiveness of Facemasks in Reducing the Spread of the Severe Acute Respiratory Syndrome – Coronavirus 2 (SARS-Cov-2) in Uganda 

Title: Universal Masking is Urgent in the COVID-19 Pandemic: SEIR and Agent Based Models, Empirical Validation, Policy Recommendations

Title: Face Masks Against COVID-19: An Evidence Review

Title: Could Masks Curtail the Post-lockdown Resurgence of COVID-19 in the US?

Title: Quantifying Respiratory Airborne Particle Dispersion Control Through Improvised Reusable Masks

The following are links to experimental work that has been reported on, but yet to be formalized into a paper.

Wake Forest, testing of homemade cloth face masks

Oh, and have you had people tell you that the New England Journal of Medicine is against mask wearing in public? Well, they’re either lying or expressing their ignorance and inability to do a little research. Besides what they’ve published above, see this:

Universal Masking in the COVID-19 Era

“Facemasking is the single most effective strategy to reduce COVID transmission” –  Jennifer Kasten, MD

3 Responses to “Face Masks – A Summary of Relevant Research Papers for COVID-19”


  1. Face Masks and the Christian | Sound Reason & More - June 13, 2020

    […] UPDATE 6/13: All future updates on new studies will be found here. […]

  2. On Masks: Notes for Rebuttal – Another Logical Take - July 24, 2020

    […] “Face Masks – A Summary of Relevant Research Papers for COVID-19.” Sound Reason & More,June 11, 2020, https://soundreasonandmore.wordpress.com/2020/06/11/face-masks-a-summary-of-relevant-research-papers…. […]

  3. Why Do You Have to Wear A Mask in Class? – Another Logical Take - August 4, 2020

    […] [37] For more such evidence, see “Face Masks – A Summary of Relevant Research Papers for COVID-19,” Sound Reason & More,June 11, 2020, https://soundreasonandmore.wordpress.com/2020/06/11/face-masks-a-summary-of-relevant-research-papers…. […]

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