Mask Facts
curated by Marilyn M. Singleton, M.D., J.D. – http://marilynsingletonmdjd.com/
Updated September 26, 2020
Introduction
COVID-19 is as politically-charged as it is infectious. Early in the COVID-19 pandemic, the WHO, the CDC and NIH’s Dr. Anthony Fauci discouraged wearing masks as not useful for non-health care workers. Now they recommend wearing cloth face coverings in public settings where other social distancing measures are hard to do (e.g., grocery stores and pharmacies). The recommendation was published without a single scientific paper or other information provided to support that cloth masks actually provide any respiratory protection. Let’s look at the data.
The theory behind mask wearing:
Source control: Cloth mask can trap droplets that come out of a person’s mouth when they cough or sneeze.
Protection: Personal Protective Equipment (PPE) – only N95 masks
Transmission of SARS-CoV-2
Note: A COVID-19 (SARS-CoV-2) particle is 0.125 micrometers/microns (μm); influenza virus size is 0.08 – 0.12 μm; a human hair is about 150 μm.
*1 nm = 0.001 micron; 1000 nm = 1 micron; Micrometer (μm) is the preferred name for micron
*1 meter is = 1,000,000,000 [trillion] nm or 1,000,000 [million] microns
*For a complete dissection and explanation of aerosols and airborne particles, please see Understanding Particle Size and Aerosol-based Transmission by Steve Probst. https://www.4cconference.com/wp-content/uploads/2020/07/Understanding-Particle-Size-and-Aerosol-Based-Transmission.pdf
Droplets
Virus is transmitted through respiratory droplets produced when an infected person coughs, sneezes, or talks.
Larger respiratory droplets (>5 μm) remain in the air for only a short time and travel only short distances, generally <1 meter. They fall to the ground quickly.https://www.thelancet.com/journals/lanres/article/PIIS2213-2600(20)30245-9/fulltext
This idea guides the CDC’s advice to maintain at least a 6-foot distance.
Small (<5 μm) aerosolized droplets can remain in the air for at least 3 hours and travel long distances (up to 27 ft.).
Air currents
In an air conditioned environment these large droplets may travel farther.
Ventilation. Even the opening of an entrance door and a small window can dilute the number of small droplets to one half after 30 seconds. (This study looked at droplets from uninfected persons). This is clinically relevant because poorly ventilated and populated spaces, like public transport and nursing homes, have high SARS-CoV-2 disease transmission despite physical distancing.
Humidity
Since 1961, experiments showed that viral-pathogen-carrying droplets were inactivated within shorter and shorter times as ambient humidity was increased. Dryness drives the small aerosol particles. See e.g., review of studies, https://aaqr.org/articles/aaqr-20-06-covid-0302
Conclusions
The preponderance of scientific evidence supports that aerosols play a critical role in the transmission of SARS-CoV-2. Years of dose response studies indicate that if anything gets through, you will become infected.
Thus, any respiratory protection respirator or mask must provide a high level of filtration and fit to be highly effective in preventing the transmission of SARS-CoV-2. (Works for Mycobacterium tuberculosis (3μm)
Public health authorities define a significant exposure to COVID-19 as face-to-face contact within 6 feet with a patient with symptomatic COVID-19 that is sustained for at least a few minutes (and some say more than 10 minutes or even 30 minutes).
The chance of catching COVID-19 from a passing interaction in a public space is therefore minimal.
MASKS
Filter Efficiency and Fit
Data from a University of Illinois at Chicago review https://www.cidrap.umn.edu/news-perspective/2020/04/commentary-masks-all-covid-19-not-based-sound-data
HEPA (high efficiency particulate air) filters are 99.97 to 100% efficient. HEPA filters are tested with particles that are 0.125 μm (the size of SARS-CoV-2).
Masks and respirators work by collecting particles through several physical mechanisms, including diffusion (small particles) and interception and impaction (large particles).
Surgical masks are loose-fitting devices that were designed to be worn by medical personnel to protect accidental contamination of patient wounds, and to protect the wearer against splashes or sprays of bodily fluids. They aren’t effective at blocking particles smaller than 100 μm. https://multimedia.3m.com/mws/media/957730O/respirators-and-surgical-masks-contrast-technical-bulletin.pdf
OSHA/CDC: A surgical mask is not a respirator. It cannot be used to protect workers who perform or assist with aerosol-generating procedures, which may create very fine aerosol sprays. A surgical mask can only be used to protect workers from contact with the large droplets made by patients when they cough, sneeze, talk or breathe. https://www.osha.gov/dts/guidance/flu/healthcare.html
Laboratory Studies
N95 filtering facepiece respirators (FFRs) are constructed from electret (a dielectric material that has a quasi-permanent electric charge.) An electret generates internal and external electric fields so the filter material has electrostatic attraction for additional collection of all particle sizes. As flow increases, particles will be collected less efficiently.
A properly fitted N95 will block 95% of tiny air particles down to
0.3 μm from reaching the wearer’s face.https://www.honeywell.com/en-us/newsroom/news/2020/03/n95-masks-explained.
Problem: no source control. An N95 does not filter exhaled air passing through the exhaust/exhalation valve (for easier breathing and less moisture inside the mask).
Study measuring filter efficiency (2010)
https://academic.oup.com/annweh/article/54/7/789/202744; https://www.cidrap.umn.edu/news-perspective/2020/04/commentary-masks-all-covid-19-not-based-sound-data; https://academic.oup.com/annweh/article/54/7/789/202744
Filter efficiency was measured across a wide range of small particle sizes (0.02 to 1 µm) at 33 and 99 L/min.
All the cloth masks and materials had near zero efficiency at 0.3 µm, a particle size that easily penetrates into the lung (SARS-CoV-2 is 0.125 µm)
Efficiency for the entire range of particles
T-shirts — 10%
Scarves — 10% to 20%
Cloth masks — 10% to 30%
Sweatshirts — 20% to 40%
Towels — 40%
Study measuring filter efficiency (2014, Korea)
Evaluated 44 masks, respirators, and other materials with similar methods and small aerosols (0.08 and 0.22 µm)
N95 FFR filter — >95% efficiency
Medical masks — 55% efficiency
General (cloth) masks — 38% efficiency
Handkerchiefs — 2% (one layer) to 13% (four layers) efficiency.
Conclusion: Wearing masks (other than N95) will not be effective at preventing SARS-CoV-2 transmission, whether worn as source control or as PPE.
N95s protect health care workers, but are not recommended for source control transmission.
Surgical masks are better than cloth but not very efficient at preventing emissions from infected patients. Cloth masks must be 3 layers, plus adding static electricity by rubbing with rubber glove.
The cloth that serves as the filtration for the mask is meant to trap particles being breathed in and out. But it also serves as a barrier to air movement because it forces the air to take the path of least resistance, resulting in the aerosols going in and out at the sides of the mask.
An August 2020 UCSF study suggested that the mask would decrease the absolute volume of the inoculum. (The concentrations of bacteria upstream and downstream of the test devices were measured with an aerodynamic size spectrometer) https://ucsf.app.box.com/s/blvolkp5z0mydzd82rjks4wyleagt036
Human Studies
Study of correct use of masks (2020, Singapore).
https://www.medpagetoday.com/infectiousdisease/publichealth/86601
Overall, data were collected from 714 men and women. Of all ages, only 90 participants (12.6%) passed the visual mask fit test. About 75% performed strap placement incorrectly, 61% left a “visible gap between the mask and skin,” and about 60% didn’t tighten the nose-clip.
Study of surgical face mask use in health care workers (2009, Japan).
Masks did not provide benefit in terms of cold symptoms or getting cold.
Randomized clinical trial of standard medical/surgical masks in health care workers (2010, Australia).
Study was spurred by the H1N1 flu. While N95 masks offered protection against respiratory illness, medical mask wearers and control group numbers were similar.
Review of influenza virus and face masks in health care workers (HCWs) (2010, Hong Kong).
6 studies of face mask use, both surgical masks and N-95 respirators in HCWs and community settings. The effectiveness of face masks is probably impacted by compliance issues in both the healthcare and community setting. Various studies show a lower level of compliance with face masks or find lower reported acceptability of face masks compared to hand hygiene behaviors and other non-pharmaceutical interventions.
Review of masks against influenza (2012, Europe).
https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1750-2659.2011.00307.x
17 eligible studies. One study had improvement with mask plus hand sanitizer. None of the studies established a conclusive relationship between mask ⁄ respirator use and protection against influenza infection.
*The first randomized controlled trial of cloth masks in health care workers (2015, Australia).
https://bmjopen.bmj.com/content/5/4/e006577; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4420971/pdf/bmjopen-2014-006577.pdf
Penetration of:
Cloth masks by particles — 97%
Medical masks — 44%,
3M Vflex 9105 N95 — 0.1%
3M 9320 N95 — <0.01%
Cloth masks resulted in significantly higher rates of infection than medical masks, and also performed worse than the control arm some of whom may have worn masks.
The virus may survive on the surface of the face masks
Self-contamination through repeated use and improper doffing is possible. A contaminated cloth mask may transfer pathogen from the mask to the bare hands of the wearer.
Moisture retention, reuse of cloth masks, and poor filtration may result in increased risk of infection.
Cloth masks should not be recommended for health care workers, particularly in high-risk situations.
Review of N95 and surgical masks against respiratory infection (2016). https://www.cmaj.ca/content/cmaj/188/8/567.full.pdf
From January 1990 to December 2014. 6 clinical studies: 3 randomized controlled trials (RCTs), 1 cohort study and 2 case–control studies, and 23 surrogate exposure studies.
In the meta-analysis of the clinical studies, “no significant difference between N95 respirators and surgical masks in associated risk of (a) laboratory-confirmed respiratory infection, (b) influenza-like illness, or (c) reported work-place absenteeism.”
Review of masks and N95s against respiratory infection (2017, Singapore).
Separate meta-analyses of 6 randomized controlled trials (RCTs) and 23 observational studies conducted during the 2003 SARS pandemic.
Compared to medical masks, N95 respirators provided greater protection against clinical respiratory illness (CRI) and bacterial respiratory illness (BRI). These 2 outcomes were common in these trials (average risks of 8.7% and 7.3%, respectively).
Compared to masks, N95 respirators conferred superior protection against clinical respiratory illness and laboratory-confirmed bacterial, but not viral infections or influenza life illness (ILI).
Self-reported assessment of clinical outcomes was prone to bias.
Evidence of a protective effect of masks or respirators against verified respiratory infection was not statistically significant (compared to no mask)
Randomized Controlled Trial: N95s vs medical masks in health care workers (HCWs) against influenza (2019).
2862 randomized participants, 2371 completed the study and accounted for 5180 HCW-seasons.
Among outpatient health care personnel, N95 respirators (8.2%) vs medical masks (7.2%) resulted in no significant difference in the incidence of laboratory-confirmed influenza. 90% said they wore the mask all the time.
Review of N95 respirators versus surgical masks against influenza (March 2020, China).
6 randomized controlled trials (RCTs) involving 9,171 participants were included (2015-2020). There were no statistically significant differences in preventing laboratory-confirmed influenza, laboratory-confirmed respiratory viral infections, laboratory-confirmed respiratory infection and influenza-like illness using N95 respirators and surgical masks.
Meta-analysis indicated a protective effect of N95 respirators against laboratory-confirmed bacterial colonization.
CDC Review since 1946 of masks and influenza (May 2020)
Nonpharmaceutical Measures for Pandemic Influenza in Nonhealthcare Settings—Personal Protective and Environmental Measures.” https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article
Systematic review. 10 RCTs that reported estimates of the effectiveness of face masks in reducing laboratory-confirmed influenza virus infections in the community from literature published during 1946–July 27, 2018.
There is limited evidence for face masks’ effectiveness in preventing laboratory-confirmed influenza virus transmission either when worn by the infected person for source control or when worn by uninfected persons to reduce exposure.
“Proper use of face masks is essential because improper use might increase the risk for transmission.”
A study of 4 patients (July 2020, South Korea).
Known patients infected with SARS-CoV-2 wore masks and coughed into a Petrie dish. “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.”
Studied different types of face coverings in non-clinical setting (August 2020).
They used a black box, a laser, and a camera. A person wears a face mask and speaks into the direction of an expanded laser beam inside a dark enclosure. Droplets that propagate through the laser beam scatter light, which is recorded with a camera. A simple computer algorithm then counts the droplets seen in the video.
The N95 led to a droplet transmission of below 0.1%.
Cotton and polypropylene masks, some of which were made from apron material showed a droplet transmission ranging from 10% to 40%.
Knitted mask had up to 60% droplet transmission.
Neck fleece had 110% droplet transmission (10% higher than not wearing a mask).
Speaking through some masks (particularly the neck fleece, bandanas) seemed to disperse the largest droplets into a multitude of smaller droplets … which explains the apparent increase in droplet count relative to no mask in that case.
See “Positive Effects of Masks” below. A recent study suggested that the mask would decrease the absolute volume of the inoculum. (The concentrations of bacteria upstream and downstream of the test devices were measured with an aerodynamic size spectrometer) https://ucsf.app.box.com/s/blvolkp5z0mydzd82rjks4wyleagt036
Austrian observation (August 2020)
https://corona-transition.org/maskenpflicht-brachte-in-osterreich-keinerlei-messbaren-nutzen (in German)
The introduction, retraction and re-introduction of mandatory face masks in Austria had no influence at all on the infection rate.
News report (August 13, 2020)
https://sentinelksmo.org/more-deception-kdhe-hid-data-to-justify-mask-mandate/
In Kansas, the 90 counties without mask mandates had lower coronavirus infection rates than the 15 counties with mask mandates. To hide this fact, the Kansas health department tried to manipulate the official statistics and data presentation.
