COMMENTARY: Masks-for-all for COVID-19 not based on sound data

Dr. Brosseau is a national adept on respiratory auspices and infectious diseases and professor ( retired ), University of Illinois at Chicago.
Dr. Sietsema is besides an technical on respiratory security and an adjunct professor at the University of Illinois at Chicago. _____________________________________ Editor’s Note: The authors added the follow argument on Jul 16. The authors and CIDRAP have received requests in late weeks to remove this article from the CIDRAP web site. Reasons have included : ( 1 ) we don ’ metric ton rightfully know that fabric masks ( face coverings ) are not effective, since the data are so restrict, ( 2 ) wearing a fabric disguise or face cover is better than doing nothing, ( 3 ) the article is being used by individuals and groups to support non-mask wear where mandated and ( 4 ) there are nowadays many modeling studies suggesting that fabric masks or confront coverings could be effective at flattening the curve and preventing many cases of infection.

If the data are limited, how can we say face coverings are likely not effective?

We agree that the data supporting the effectiveness of a fabric masquerade or face covering are very restrict. We do, however, have data from testing ground studies that indicate cloth masks or face coverings offer very first gear filter solicitation efficiency for the smaller inhalable particles we believe are largely creditworthy for infection, peculiarly from pre- or asymptomatic individuals who are not coughing or sneezing. At the time we wrote this article, we were unable to locate any well-performed studies of fabric dissemble escape when wear on the face—either in or outward escape. vitamin a far as we know, these data are distillery lacking. The guidelines from the Centers for Disease Control and Prevention ( CDC ) for font coverings initially did not have any citations for studies of fabric fabric efficiency or suit, but some references have been added since the guidelines were first posted. We reviewed these and found that many employ very crude, non-standardized methods ( Anfinrud 2020, Davies 2013, Konda 2020, Aydin 2020, Ma 2020 ) or are not relevant to cloth face coverings because they evaluate respirators or surgical masks ( Leung 2020, Johnson 2009, Green 2012 ). The CDC failed to reference the National Academies of Sciences Rapid Expert Consultation on the Effectiveness of Fabric Masks for the COVID-19 Pandemic ( NAS 2020 ), which concludes, “ The evidence from…laboratory filtration studies suggests that such framework masks may reduce the transmission of larger respiratory droplets. There is small attest regarding the transmission of small aerosolize particulates of the size potentially exhaled by asymptomatic or preclinical individuals with COVID-19. ” As well, the CDC neglected to mention a well-done study of fabric corporeal percolate performance by Rengasamy et aluminum ( 2014 ), which we reviewed in our article .

Is wearing a face covering better than nothing?

Wearing a fabric mask or confront cover could be better than doing nothing, but we simply don ’ thyroxine know at this point. We have observed an development in the message around cloth masks, from an initial agreement that they should not be seen as a replacement for physical distance to more late message that suggests cloth masks are equivalent to physical distance. And while everyone appears to understand that this messaging suggests that a fabric mask is appropriate merely for reservoir manipulate ( internet explorer, to protect others from infection ), holocene CDC and early guidance recommending their function by workers seems to imply that they offer some type of personal protection. We know of workplaces in which employees are told they can not wear respirators for the hazardous environments they work in, but alternatively need to wear a fabric mask or face covering. These are dangerous and inappropriate applications that greatly exceed the initial determination of a fabric mask. We are concerned that many people do not understand the very limit degree of protection a fabric dissemble or face covering likely offers as reservoir dominance for people located nearby .

Do we support cloth mask wearing where mandated?

Despite the current limited scientific data detailing their potency, we support the break of confront coverings by the public when mandated and when in close liaison with people whose infection status they do n’t know. however, we besides encourage everyone to continue to limit their time spent indoors near potentially infectious people and to not count on or expect a fabric mask or face covering to protect them or the people around them. The pandemic is not over and will not probably be over for some meter. As states and local jurisdictions reopen, we encourage people to continue to assess and limit their risks. Cloth masks and face coverings probably do not offer the same degree of auspices as forcible outdistance, isolation, or limiting personal liaison time .

Will face coverings ‘flatten the curve’ and stop the pandemic?

We have reviewed the many modeling studies that purport to demonstrate that fabric masks or face coverings have the electric potential for flattening the bend or significantly decrease the number of cases. These studies fail to recognize respective crucial facts :

  • The filter performance of a cloth material does not directly translate or represent its performance on an individual, because it neglects the understanding of fit.
  • Cloth masks or coverings come in a variety of shapes, sizes, and materials and are not made according to any standards.
  • Transmission is not simply a function of short random interactions between individuals, but rather a function of particle concentration in the air and the time exposed to that concentration.
  • A cloth mask or face covering does very little to prevent the emission or inhalation of small particles. As discussed in an earlier CIDRAP commentary and more recently by Morawska and Milton (2020) in an open letter to WHO signed by 239 scientists, inhalation of small infectious particles is not only biologically plausible, but the epidemiology supports it as an important mode of transmission for SARS-CoV-2, the virus that causes COVID-19.

In compendious, though we support mask wearing by the general public, we continue to conclude that fabric masks and face coverings are probably to have limited impact on lowering COVID-19 transmission, because they have minimal ability to prevent the emission of modest particles, offer limited personal protective covering with deference to little particle inhalant, and should not be recommended as a refilling for forcible outdistance or reducing time in enclosed spaces with many potentially infectious people. We are identical concerned about messaging that suggests cloth masks or face coverings can replace physical distance. We besides worry that the public does n’t understand the limitations of fabric masks and confront coverings when we observe how many people wear their mask under their nose or even under their mouthpiece, remove their masks when talking to person nearby, or fail to practice physical distance when wearing a mask .


Anfinrud P, Stadnytskyi V, Bax CE, et al. Visualizing speech-generated oral fluid droplets with laser light scattering. N Engl J Med 2020 ( published online Apr 15 ) Davies A, Thompson KA, Giri K, et al .   Testing the efficacy of homemade masks : would they protect in an influenza pandemic ? Disaster Med Public Health Prep 2013 Aug ; 7 ( 4 ) :413-8 Green CF, Davidson CS, Panlilio AL, et al. Effectiveness of selected surgical masks in arresting vegetative cells and endospores when worn by simulate catching patients. Infect Control Hosp Epidemiol 2012 May ; 33 ( 5 ) :487‐94 Johnson DF, Druce JD, Birch C, et al. A quantitative appraisal of the efficacy of surgical and N95 masks to filter influenza virus in patients with acute influenza infection. Clin Infect Dis 2009 Jul 15 ; 49 ( 2 ) :275-7 Konda A, Prakash A, Moss GA, et al. Aerosol filtration efficiency of common fabrics used in respiratory fabric masks. ACS Nano. 2020 ( published online Apr 24 ) Leung NHL, Chu DKW, Shiu EYC, et al. Respiratory virus shedding in exhale breath and efficacy of face masks. Nat Med 2020 ( published online Apr 3 ) Ma QX, Shan H, Zhang HL, et al. Potential utilities of mask-wearing and moment pass hygiene for fighting SARS-CoV-2. J Med Virol 2020 ( published online Mar 31 ) Morawska L, Milton DK. It is time to address airborne infection of COVID-19. Clin Infect Dis 2020 ( published online Jul 6 ) National Academies of Sciences, Engineering, and Medicine. 2020. Rapid expert consultation on the effectiveness of fabric masks for the COVID-19 pandemic. Washington, DC, National Academies Press. Apr 8, 2020 Rengasamy S, Eimer B, Szalajda J. A quantitative judgment of the total inward escape of NaCl aerosol representing submicron-size bioaerosol through N95 filtering facepiece respirators and surgical masks. J Occup Environ Hyg 2014 May 9 ; 11 ( 6 ) :388-96 _________________________________________________________________ Editor’s Note: besides on Jul 16, The following text was changed immediately after the “ surgical masks as source manipulate ” subheading in the original comment : master : family studies find very express effectiveness of surgical masks at reducing respiratory illness in early family members.22-25 Updated : We were able to identify only two family studies in which surgical masks were worn by the index affected role merely, as source control.24,25 Neither of these found a significant shock on junior-grade disease transmission, although both studies had authoritative limitations. The original citation 24 ( bin-Reza 2011 ) was changed to Canini 2010. In an unrelated correction on Jul 16, mention 45 was faulty and now correctly cites bin-Reza 2012. __________________________________________________________________ In reaction to the flow of misinformation and misunderstanding about the nature and function of masks and respirators as source control or personal protective equipment ( PPE ), we critically review the subject to inform ongoing COVID-19 decision-making that relies on science-based data and professional expertness. As noted in a previous comment, the limited data we have for COVID-19 powerfully support the possibility that SARS-CoV-2—the virus that causes COVID-19—is transmitted by inhalant of both droplets and aerosols near the reservoir. It is besides likely that people who are pre-symptomatic or asymptomatic throughout the duration of their infection are spreading the disease in this way .

Data lacking to recommend broad mask use

We do not recommend requiring the cosmopolitan public who do not have symptoms of COVID-19-like illness to routinely wear fabric or surgical masks because :

  • There is no scientific evidence they are effective in reducing the risk of SARS-CoV-2 transmission
  • Their use may result in those wearing the masks to relax other distancing efforts because they have a sense of protection
  • We need to preserve the supply of surgical masks for at-risk healthcare workers.

Sweeping mask recommendations—as many have proposed—will not reduce SARS-CoV-2 transmittance, as evidenced by the widespread exercise of wearing such masks in Hubei state, China, before and during its batch COVID-19 transmittance feel earlier this year. Our review of relevant studies indicates that fabric masks will be ineffective at preventing SARS-CoV-2 transmission, whether worn as source command or as PPE. surgical masks probably have some utility program as source control ( meaning the wearer limits virus dispersion to another person ) from a diagnostic patient in a healthcare setting to stop the ranch of large cough particles and limit the lateral pass distribution of cough particles. They may besides have very limited utility as source command or PPE in households. Respirators, though, are the only option that can ensure protection for frontline workers dealing with COVID-19 cases, once all of the strategies for optimizing respirator issue have been implemented. We do not know whether respirators are an effective treatment as generator control for the public. A non-fit-tested respirator may not offer any better protection than a surgical mask. Respirators work as PPE only when they are the mighty size and have been fit-tested to demonstrate they achieve an adequate protection component. In a time when respirator supplies are circumscribed, we should be saving them for frontline workers to prevent infection and remain in their jobs. These recommendations are based on a review of available literature and informed by professional expertness and reference. We outline our review criteria, summarize the literature that best addresses these criteria, and describe some activities the public can do to help “ flatten the wind ” and to protect frontline workers and the general public. We realize that the public yearns to help protect medical professionals by contributing homemade masks, but there are better ways to help .

Filter efficiency and fit are key for masks, respirators

The best attest of mask and gasmask performance starts with testing filter efficiency and then evaluating fit ( facepiece escape ). Filter efficiency must be measured beginning. If the trickle is ineffective, then fit will be a measuring stick of trickle efficiency only and not what is being leaked around the facepiece .

Filter efficiency

Masks and respirators work by collecting particles through respective physical mechanisms, including dissemination ( small particles ) and interception and impaction ( large particles ) .1 N95 filtering facepiece respirators ( FFRs ) are constructed from electret filter substantial, with electrostatic attraction for extra collection of all atom sizes.2 Every filter has a particle size range that it collects inefficiently. Above and below this range, particles will be collected with greater efficiency. For hempen non-electret filters, this size is about 0.3 micrometers ( µm ) ; for electret filters, it ranges from 0.06 to 0.1 µm. When testing, we care most about the point of inefficiency. As flow increases, particles in this range will be collected less efficiently. The best filter tests use worst-case conditions : high flow rates ( 80 to 90 liters per moment [ L/min ] ) with particle sizes in the least efficiency roll. This guarantees that filter efficiency will be high at distinctive, lower flow rates for all particle sizes. Respirator filter certification tests use 84 L/min, well above the distinctive 10 to 30 L/min breathe rates. The N95 designation means the filter exhibits at least 95 % efficiency in the least efficient particle size roll. Studies should besides use well-characterized inert particles ( not biological, anthropogenetic, or naturogenic ones ) and instruments that quantify concentrations in narrow size categories, and they should include an N95 FFR or like gasmask as a positive control .


Fit should be a meter of how well the mask or respirator prevents leakage around the facepiece, as noted earlier. Panels of representative homo subjects reveal more about fit than tests on a few individuals or mannequins.

quantitative suit tests that measure concentrations inside and outside of the facepiece are more discriminating than qualitative ones that rely on taste or olfactory property .

Mask, N95 respirator filtering performance

Following a recommendation that fabric masks be explored for habit in healthcare settings during the adjacent influenza pandemic,3 The National Institute for Occupational Safety and Health ( NIOSH ) conducted a study of the filter operation on invest materials and articles, including commercial fabric masks marketed for air befoulment and allergens, sweatshirts, t-shirts, and scarfs.4 Filter efficiency was measured across a broad range of little particle sizes ( 0.02 to 1 µm ) at 33 and 99 L/min. N95 respirators had efficiencies greater than 95 % ( as expected ). For the entire compass of particles tested, t-shirts had 10 % efficiency, scarves 10 % to 20 %, fabric masks 10 % to 30 %, sweatshirts 20 % to 40 %, and towels 40 %. All of the fabric masks and materials had near zero efficiency at 0.3 µm, a particle size that easily penetrates into the lungs.4 Another study evaluated 44 masks, respirators, and other materials with alike methods and small aerosols ( 0.08 and 0.22 µm ) .5 N95 FFR filter efficiency was greater than 95 %. medical masks exhibited 55 % efficiency, general masks 38 % and handkerchiefs 2 % ( one layer ) to 13 % ( four layers ). These studies demonstrate that fabric or homemade masks will have identical low filter efficiency ( 2 % to 38 % ). medical masks are made from a wide range of materials, and studies have found a across-the-board range of percolate efficiency ( 2 % to 98 % ), with most exhibiting 30 % to 50 % efficiency.6-12 We reviewed other filter efficiency studies of makeshift fabric masks made with versatile materials. Limitations included challenge aerosols that were ill characterized13 or besides large14-16 or stream rates that were besides low.17

Mask and respirator fit

Regulators have not developed guidelines for fabric or surgical mask match. N95 FFRs must achieve a fit component ( outside divided by inside concentration ) of at least 100, which means that the facepiece must lower the outside assiduity by 99 %, according to the OSHA respiratory security standard. When fit is measured on a mask with inefficient filters, it is very a measure of the collection of particles by the filter plus how well the mask prevents particles from leaking around the facepiece. several studies have measured the match of masks made of fabric and other homemade materials.13,18,19 We have not used their results to evaluate mask operation, because none measured filter efficiency or include respirators as positive controls. One study of surgical masks showing relatively high efficiencies of 70 % to 95 % using NIOSH test methods measured total mask efficiencies ( trickle plus facepiece ) of 67 % to 90 % .7 These results illustrate that surgical masks, even with relatively effective filters, do not fit well against the face. In total, fabric masks exhibit very low filter efficiency. Thus, even masks that match well against the face will not prevent inhalant of small particles by the wearer or emission of small particles from the wearer. One study of surgical mask meet described above suggests that inadequate paroxysm can be reasonably offset by good filter collection, but will not approach the degree of protective covering offered by a gasmask. The problem is, however, that many surgical masks have identical hapless filter operation. surgical masks are not evaluated using worst-case trickle tests, so there is no way to know which ones offer better filter efficiency .

Studies of performance in real-world settings

Before recommending them, it ‘s important to understand how masks and respirators perform in households, healthcare, and other settings .

Cloth masks as source control

A historical overview of fabric masks notes their use in US healthcare settings starting in the late 1800s, first as reservoir see on patients and nurses and late as PPE by nurses.20 Kellogg,21 seeking a argue for the failure of fabric masks required for the public in stopping the 1918 influenza pandemic, found that the number of fabric layers needed to achieve acceptable efficiency made them unmanageable to breathe through and caused escape around the dissemble. We found no well-designed studies of fabric masks as source master in family or healthcare settings. In total, given the dearth of information about their performance as generator control in real-world settings, along with the highly moo efficiency of fabric masks as filters and their inadequate match, there is no evidence to support their use by the populace or healthcare workers to control the emission of particles from the wearer .

Surgical masks as source control

We were able to identify only two family studies in which surgical masks were worn by the index affected role only, as reservoir control.24,25 Neither of these found a meaning impact on secondary coil disease transmission, although both studies had crucial limitations. clinical trials in the operating room dramaturgy have found no difference in hoist contagion rates with and without surgical masks.26-29 Despite these findings, it has been unmanageable for surgeons to give up a long-standing practice.30 There is evidence from testing ground studies with coughing infectious subjects that surgical masks are effective at preventing emission of big particles31-34 and minimizing lateral dispersion of cough particles, but with coincident displacement of aerosol emission upward and downward from the mask.35 There is some evidence that surgical masks can be effective at reducing overall particle emission from patients who have multidrug-resistant tuberculosis,36 cystic fibrosis,34 and influenza.33 The latter found surgical masks decreased discharge of large particles ( larger than 5 µm ) by 25-fold and small particles by double from flu-infected patients.33 Sung37 found a 43 % decrease in respiratory viral infections in stem-cell patients when everyone, including patients, visitors, and healthcare workers, wear surgical masks. In summarize, wearing surgical masks in households appears to have very small affect on transmission of respiratory disease. One possible reason may be that masks are not likely worn endlessly in households. These data suggest that surgical masks worn by the public will have no or very low affect on disease transmission during a pandemic. There is no evidence that surgical masks worn by healthcare workers are effective at limiting the emission of little particles or in preventing contaminant of wounds during operation. There is moderate tell that surgical masks worn by patients in healthcare settings can lower the discharge of large particles generated during cough and specify attest that belittled particle emission may besides be reduced .

N95 FFRs as source control

respirator habit by the populace was reviewed by NIOSH : ( 1 ) untrained users will not wear respirators correctly, ( 2 ) non-fit tested respirators are not likely to fit, and ( 3 ) improvised fabric masks do not provide the level of security of a fit-tested respirator. There are few studies examining the potency of respirators on patients. An N95 FFR on coughing human subjects showed greater effectiveness at limiting lateral particle dispersion than surgical masks ( 15 curium and 30 centimeter distribution, respectively ) in comparison to no mask ( 68 curium ). 35 cystic fibrosis patients reported that surgical masks were tolerable for short periods, but N95 FFRs were not.34 In summary, N95 FFRs on patients will not be effective and may not be appropriate, peculiarly if they have respiratory illness or other fundamental health conditions. Given the stream extreme shortages of respirators needed in healthcare, we do not recommend the use of N95 FFRs in public or family settings .

Cloth masks as PPE

A randomized trial comparing the effect of medical and fabric masks on healthcare proletarian illness found that those wearing fabric masks were 13 times more likely to experience influenza-like illness than those wearing checkup masks.38 In sum, very poor filter and fit performance of fabric masks described earlier and very humble potency for fabric masks in healthcare settings lead us conclude that fabric masks offer no protection for healthcare workers inhaling infectious particles near an infect or confirmed affected role .

Surgical masks as PPE

several randomized trials have not found any statistical remainder in the efficacy of surgical masks versus N95 FFRs at lowering infectious respiratory disease outcomes for healthcare workers.39-43 Most reviews have failed to find any advantage of one interposition over the other.23,44-48 Recent meta-analyses found that N95 FFRs offered higher protection against clinical respiratory illness49,50 and lab-confirmed bacterial infections,49 but not viral infections or influenza-like illness.49 A recent pool analysis of two earlier trials comparing medical masks and N95 filtering facepiece respirators with controls ( no protection ) found that healthcare workers endlessly wearing N95 FFRs were 54 % less likely to experience respiratory viral infections than controls ( P = 0.03 ), while those wearing aesculapian masks were only 12 % less probably than controls ( P = 0.48 ; resultant role is not importantly unlike from zero ) .51 While the data supporting the use of surgical masks as PPE in real-world settings are limited, the two meta-analyses and the most recent randomized controlled study51 combined with evidence of moderate filter efficiency and complete lack of facepiece fit lead us to conclude that surgical masks offer very low levels of protection for the wearer from aerosol inhalant. There may be some protection from droplets and liquids propelled immediately onto the mask, but a faceshield would be a better choice if this is a concern .

N95 FFRs as PPE

A retrospective cohort learn found that nurses ‘ risk of SARS ( severe acute respiratory syndrome, besides caused by a coronavirus ) was lower with reproducible use of N95 FFRs than with consistent use of a surgical mask.52 In total, this study, the meta-analyses, randomized controlled trial report above,49,51 and testing ground data showing high filter efficiency and high accomplishable fit factors lead us to conclude that N95 FFRs offer lake superior protection from inhalable infectious aerosols likely to be encountered when caring for suspected or confirmed COVID-19 patients. The precautionary principle supports higher levels of respiratory protection, such as powered air-purifying respirators, for aerosol-generating procedures such as cannulation, bronchoscopy, and acquiring respiratory specimens .


While this is not an exhaustive reappraisal of masks and respirators as source control and PPE, we made our best campaign to locate and review the most relevant studies of testing ground and real-world performance to inform our recommendations. Results from lab studies of trickle and equip performance inform and support the findings in real-world settings. Cloth masks are ineffective as beginning control and PPE, surgical masks have some function to play in preventing emissions from infect patients, and respirators are the best choice for protecting healthcare and early frontline workers, but not recommended for generator control. These recommendations apply to pandemic and non-pandemic situations. Leaving aside the fact that they are ineffective, telling the public to wear fabric or surgical masks could be interpreted by some to mean that people are safe to stop isolating at home plate. It ‘s besides late now for anything but stopping adenine a lot person-to-person interaction as possible. Masks may confuse that message and give people a fake sense of security. If masks had been the solution in Asia, should n’t they have stopped the pandemic before it spread elsewhere ?

Ways to best protect health workers

We recommend that healthcare organizations follow US Centers for Disease Control and Prevention ( CDC ) guidance by moving first through conventional, then eventuality, and ultimately crisis scenarios to optimize the supply of respirators. We recommend using the CDC ‘s burn rate calculator to help identify areas to reduce N95 consumption and working down the CDC checklist for a strategic approach to extend N95 issue. For readers who are disappointed in our recommendations to stop making fabric masks for themselves or healthcare workers, we recommend alternatively pitching in to locate N95 FFRs and other types of respirators for healthcare organizations. Encourage your local or state government to organize and reach out to industries to locate respirators not presently being used in the non-healthcare sector and align contribution efforts to frontline health workers .


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