UP-TO-DATE SCIENCE 

Facemask Literature Summary

(Science Says Masks Don't Protect Against Respiratory Viruses)

Dr. Philip Buckler

 

It is easy to find laboratory studies, theoretical computer models based on those laboratory studies, and opinion pieces which predict that masks should provide some protection against respiratory viral infections, but real-world randomized controlled trials, cross-sectional studies, observational studies and meta-analyses have at best provided mixed or minimal evidence in favor of masks, most often failing to demonstrate any statistically significant benefit, and on multiple occasions have suggested that the use of masks may increase disease transmission depending on circumstances.

 

A strong body of definitive evidence for a statistically significant protective effect against respiratory viral infections is a necessary but not sufficient precondition for morally justifying mask mandates. Dozens of real-world studies conducted over the last 100 years have failed to provide this essential evidence, and have often produced results suggesting that there are many circumstances under which the routine wearing of masks actually increases microbial infections either in the users or those around them.

 

The following 16 studies are just a small sampling of this literature.

Reference 1

Authors

MacIntyre et al 2011, MacIntyre et al 2013, MacIntyre et al 2015

 

Type and Details:

  • Cluster-Randomized Controlled Trials

  • Series of Randomized controlled trials comparing the efficacy of medical masks and N95 masks and double-layered cotton clothmasks with medical masks.

  • Involved a total of 4,717 healthcare workers in China and Vietnam.

  • Included a convenience non-randomized nonmasked control group.

 

Results and Quotes

"The original purpose of medical masks was to prevent microbial contamination of wounds while worn by surgeons during surgery (hence their common name “surgical masks”), yet randomized controlled trials show no efficacy against wound contamination... Masks in community settings have no clearly

proved efficacy." (MacIntyre et al 2013)

 

"Cloth masks resulted in significantly higher rates of infection than medical masks, and also performed worse than the control arm." (MacIntyre et al 2015)

 

"Observations during SARS suggested double-masking and other practices increased the risk of infection because of moisture, liquid diffusion and pathogen retention." (MacIntyre et al 2015)

"...we compared rates of infection in the medical mask arm with rates observed in medical mask arms from two previous RCTs in which no efficacy of medical masks could be demonstrated when compared with control or N95 respirators." (MacIntyre et al 2015)

 

"... the rate of virus isolation in the no-mask control group in the first Chinese RCT was 3.1%, which was not significantly different to the rates of virus isolation in the medical mask arms in any of the three trials including this one." (MacIntyre et al 2015)

 

"... the magnitude of difference raises the possibility that cloth masks cause an increase in infection risk in HCWs." (MacIntyre et al 2015)

 

"... the results caution against the use of cloth masks." (MacIntyre et al 2015)

 

Significance

Represents a best-case scenario for cloth mask use, involving trained personnel and daily washings. The dramatically worse performance of cloth masks even under optimal conditions in preventing respiratory viral infections when compared to medical masks has profound implications when we take into account the multiple other studies which show medical masks conferring no benefit as either source control or personal protection.

 

If cloth masks are not recommended for healthcare workers, they should

not be forced on the general public.

 

The lack of differences in overall respiratory viral infection rates in the nonrandomized convenience no mask group in MacIntyre's 2011 study when compared with the masked groups in MacIntyre's 2011, 2013, and 2015 studies is consistent with the findings in Bundgaard's 2020 randomized controlled trial comparing medical masks vs. no masks.

 

Full Citations

MacIntyre, C. R., Q. Wang, S. Cauchemez, H. Seale, D. E. Dwyer, P. Yang, W. Shi, Z. Gao, X. Pang, Y. Zhang, X. Wang, W. Duan, B. Rahman, and N. Ferguson. "A Cluster Randomized Clinical Trial Comparing Fit-Tested and Non-Fit-Tested N95 Respirators to Medical Masks to Prevent Respiratory Virus Infection in Health Care Workers." Influenza Other Respir Viruses 5, no. 3 (May 2011): 170-9.

https://dx.doi.org/10.1111/j.1750-2659.2011.00198.x

 

MacIntyre, C. R., Q. Wang, H. Seale, P. Yang, W. Shi, Z. Gao, B. Rahman, Y. Zhang, X. Wang, A. T. Newall, A. Heywood, and D. E. Dwyer. "A Randomized Clinical Trial of Three Options for N95 Respirators and Medical Masks in Health Workers." Am J Respir Crit Care Med 187, no. 9 (May 1 2013): 960-6. https://dx.doi.org/10.1164/rccm.201207-1164OC

 

MacIntyre, C. R., H. Seale, T. C. Dung, N. T. Hien, P. T. Nga, A. A. Chughtai, B. Rahman, D. E. Dwyer, and Q. Wang. "A Cluster Randomised Trial of Cloth Masks Compared with Medical Masks in Healthcare Workers." BMJ Open 5, no. 4 (Apr 22 2015): e006577. https://dx.doi.org/10.1136/bmjopen-2014-006577

Reference 2

Author

Bundgaard et al 2020

 

Type and Details

  • Randomized Controlled Trial

  • "The Danish Facemask Study" The only Randomized Controlled Trial that has examined SARS-CoV-2 infections in masked vs. nonmasked civilian populations.

  • 4,862 participants completed the study (2,392masked; 2,470 non-masked).

Results and Quotes

The authors found no statistically significant difference in SARS-CoV-2 infection rates between the masked (1.8%) and non-masked (2.1%) study cohorts.

 

The study cohort that reported wearing the mask "exactly as instructed" had a 2.0% SARS-CoV-2 infection rate.

 

There were no statistically significant differences between the study cohorts in rates of other respiratory viral infections either.

 

"We observed no statistically significant interaction between wearers and nonwearers of eyeglasses."

 

Significance

In addition to the primary data providing evidence against the efficacy of face masks, the supplemental data collected during this study suggests that eye protection is not useful, and also conclusively demonstrates that wearing a mask for 2 months will - even in the absence of legal or social pressure - cause 16-18% of mask-wearers to shift their views to favor wearing masks in the future.

 

Full Citations

Bundgaard, H., J. S. Bundgaard, D. E. T. Raaschou-Pedersen, C. von Buchwald, T. Todsen, J. B. Norsk, M. M. Pries-Heje, C. R. Vissing, P. B. Nielsen, U. C. Winsløw, K. Fogh, R. Hasselbalch, J. H. Kristensen, A. Ringgaard, M. Porsborg Andersen, N. B. Goecke, R. Trebbien, K. Skovgaard, T. Benfield, H. Ullum, C. Torp-Pedersen, and K. Iversen. "Effectiveness of Adding a Mask Recommendation to Other Public

Health Measures to Prevent Sars-Cov-2 Infection in Danish Mask Wearers : A Randomized Controlled Trial." Ann Intern Med 174, no. 3 (Mar 2021): 335-43. https://dx.doi.org/10.7326/m20-6817

 

Reference 3

Author

Tunevall 1991

 

Type and Details

  • Randomized Controlled Trial

  • Conducted over 2 years and involved 3,088 patients.

  • Compared post-medical infection rates when operating teams wore masks vs no masks.

  • Same patient pool, same procedures, same operating rooms.

 

Results and Quotes

"After 1,537 operations performed with face masks, 73 (4.7%) wound infections were recorded and, after 1,551 operations performed without face masks, 55 (3.5%) infections occurred. This difference was not statistically significant (p > 0.05)…"

 

"It has not been possible to demonstrate any advantages for the patient when the medical team wears face masks. Therefore, the routine use of face masks ought to be reconsidered."

 

Significance

Findings from operating rooms provide strong evidence against medical masks having source control benefits.

 

Even in the operating room, medical masks provide no protection to people around the user even from bacteria which are more than 10x the size of viruses like SARS-CoV-2.

 

Bottom line: my mask does not protect you, and your mask does not

protect me.

 

Full Citations

Tunevall, T. G. "Postoperative Wound Infections and Surgical Face Masks: A Controlled Study." World J Surg 15, no. 3 (May-Jun 1991): 383-7; discussion 87-8. https://dx.doi.org/10.1007/bf01658736

 

Reference 4

Author

Chou et al 2020

 

Type and Details

  • Living Systematic Review updated quarterly

  • Survey of pertinent literature updated frequently

 

Results and Quotes

"Neither face mask use and hand hygiene nor face mask use alone was associated with a significant reduction in the rate of ILI cumulatively."

 

"Both intervention groups compared to the control showed cumulative reductions in rates of influenza over the study period, although results did not reach statistical significance."

 

Significance

No statistically significant differences between medical mask vs no mask for rates of influenza-like illness (ILI).

 

Full Citations

Aiello, A. E., G. F. Murray, V. Perez, R. M. Coulborn, B. M. Davis, M. Uddin, D. K. Shay, S. H. Waterman, and A. S. Monto. "Mask Use, Hand Hygiene, and Seasonal Influenza-Like Illness among Young Adults: A Randomized Intervention Trial." J Infect Dis 201, no. 4 (Feb 15 2010): 491-8. https://dx.doi.org/10.1086/650396

 

Aiello, Allison E., Vanessa Perez, Rebecca M. Coulborn, Brian M. Davis, Monica Uddin, and Arnold S. Monto. "Facemasks, Hand Hygiene, and Influenza among Young Adults: A Randomized Intervention Trial." PLoS One 7, no. 1 (2012): e29744.

https://dx.doi.org/10.1371/journal.pone.0029744

 

Reference 5

Authors

Aiello et al 2010

Aiello et al 2012

 

Type and Details

  • Cluster-Randomized Intervention Trials

  • Reports the results of a series of trials from 2006 to 2008 totaling 2,475 student participants living in residence halls.

 

Results and Quotes

"Neither face mask use and hand hygiene nor face mask use alone was associated with a significant reduction in the rate of ILI cumulatively."

 

"Both intervention groups compared to the control showed cumulative reductions in rates of influenza over the study period, although results did not reach statistical significance."

 

Significance

No statistically significant differences between medical mask vs no mask for rates of influenza-like illness (ILI).

 

Full Citations

Aiello, A. E., G. F. Murray, V. Perez, R. M. Coulborn, B. M. Davis, M. Uddin, D. K. Shay, S. H. Waterman, and A. S. Monto. "Mask Use, Hand Hygiene, and Seasonal Influenza-Like Illness among Young Adults: A Randomized Intervention Trial." J Infect Dis 201, no. 4 (Feb 15 2010):

491-8. https://dx.doi.org/10.1086/650396

 

Aiello, Allison E., Vanessa Perez, Rebecca M. Coulborn, Brian M. Davis, Monica Uddin, and Arnold S. Monto. "Facemasks, Hand Hygiene, and Influenza among Young Adults: A Randomized Intervention Trial." PLoS One 7, no. 1 (2012): e29744. https://dx.doi.org/10.1371/journal.pone.0029744

 

Reference 6

Authors

Barasheed et al 2014

Wang et al 2015

Alfellali et al (Preprint) 2019

 

Type and Details

  • Cluster Randomized Controlled Trials (Pilot study of 164 participants conducted in 2014 followed up by a larger study described in 2015, the results of which have been in preprint since 2019)

  • 7,851 total participants.

  • Tents of pilgrims used as the cluster randomization units.

 

Results and Quotes

Though the pilot study of 164 participants suggested a possible protective effect from medical masks, the larger study with 7,687 participants found that masks were not associated with decreased risk for infections in Hajj pilgrims with or without an infected index case within the same tent.

 

"In intention-to-treat analysis, facemask use was neither effective against laboratory-confirmed vRTIs [Viral Respiratory Tract Infections] nor against CRI [Clinical Respiratory Infections], not even in per-protocol analysis."

 

Significance

"Facemask use does not prevent clinical or laboratory-confirmed viral respiratory infections among Hajj pilgrims."

 

Full Citations

Barasheed, O., N. Almasri, A. M. Badahdah, L. Heron, J. Taylor, K. McPhee, I. Ridda, E. Haworth, D. E. Dwyer, H. Rashid, and R. Booy. "Pilot Randomised Controlled Trial to Test Effectiveness of Facemasks in Preventing Influenza-Like Illness Transmission among Australian Hajj Pilgrims in 2011." Infect Disord Drug Targets 14, no. 2 (2014): 110-6. https://dx.doi.org/10.2174/1871526514666141021112855

 

Wang, M., O. Barasheed, H. Rashid, R. Booy, H. El Bashir, E. Haworth, I. Ridda, E. C. Holmes, D. E. Dwyer, J. Nguyen-Van-Tam, Z. A. Memish, and L. Heron. "A Cluster-Randomised Controlled Trial to Test the Efficacy of Facemasks in Preventing Respiratory Viral Infection among Hajj Pilgrims." J Epidemiol Glob Health 5, no. 2 (Jun 2015): 181-9. https://dx.doi.org/10.1016/j.jegh.2014.08.002

 

Alfelali, Mohammad, Elizabeth Haworth, Osamah Barasheed, Al-Mamoon Badahdah, Hamid Bokhary, Mohamed Tashani, Mohammad Azeem, Jen Kok, Janette Taylor, Elizabeth Barnes, Haitham Bashir, Gulam Khandaker, Edward Holmes, Dominic Dwyer, Leon Heron, Godwin Wilson, Robert Booy, and Harunor Rashid. "Facemask Versus No Facemask in Preventing Viral Respiratory Infections During Hajj:

A Cluster Randomised Open Label Trial." SSRN Electronic Journal (01/01 2019). https://dx.doi.org/10.2139/ssrn.3349234 (Preprint)

 

Reference 7

Author

Al-Asmary et al 2007

 

Type and Details

  • Nested Case-control/cross-sectional study among healthcare workers

  • Evaluated the rate of respiratory infections in 250 healthcare workers serving on a Hajj medical mission.

 

Results and Quotes

"In our study regular use of facemasks offered no significant protection against ARI [Acute Respiratory Infections]. Our finding is in agreement, however, with the conclusion of the Centers for Disease Control and Prevention (CDC) in the USA which stated that surgical masks are not designed for use as particulate respirators and do not provide much protection against air-borne diseases because they do not effectively filter small particles from the air or prevent leakage around the edge of the mask when the user inhales."

 

"Furthermore, we found that intermittent use of surgical-type masks was actually associated with more than a 2.5-fold greater risk of infection. It is possible that once a facemask is worn in the presence of an infected patient, the mask could become contaminated with infectious material and touching the outside of the device could result in hand transmission of the infection to the respiratory tract during nose-rubbing."

 

Significance

"The common practice among pilgrims and medical personnel of using surgical facemasks to protect themselves against ARI [Acute Respiratory Infections] should be discontinued and regular use of alcohol-based hand scrubs should be more vigorously encouraged."

 

Full Citations

Al-Asmary, S., A. S. Al-Shehri, A. Abou-Zeid, M. Abdel-Fattah, T. Hifnawy, and T. El-Said. "Acute Respiratory Tract Infections among Hajj Medical Mission Personnel, Saudi Arabia." Int J Infect Dis 11, no. 3 (May 2007): 268-72. https://dx.doi.org/10.1016/j.ijid.2006.04.008

 

Reference 8

Author

Orr 1981

 

Type and Details

  • Observational study

  • The author compared infection rates after discontinuing the use of masks in an operating theater to infection rates recorded over the previous 4 years.

 

Results and Quotes

"No masks were worn in one operating theatre for 6 months. There was no increase in the incidence of wound infection."

 

"There was no increase in wound infections when masks were discarded in 1980; in fact there was a significant (p<o.o5) decrease. The 8 infections which did occur (Table ii) bore no relation to the throat or nose cultures from the theatre team, which from time to time yielded Staphylococcus albus or Staph.

aureus."

 

Significance

Findings provide evidence against masks having benefits for source control.

 

"The conclusion is that the wearing of a mask has very little relevance to the wellbeing of patients undergoing routine general surgery and it is a standard practice that could be abandoned."

 

Full Citations

Orr, N. W. "Is a Mask Necessary in the Operating Theatre?", Ann R Coll Surg Engl 63, no. 6 (Nov 1981): 390-2

 

Reference 9

Authors

Cowling et al 2008

Cowling et al 2009

Cowling et al 2010

 

Type and Details

  • Cluster Randomized Controlled Trial - 122 index cases and their household contacts (2008)

  • Cluster Randomized Controlled Trial - 322 index cases and their household contacts (2009)

  • Literature Review (2010)

 

Results and Quotes

Divided participants into 3 groups:

A) Control (Education)

B) Education + Hand Hygiene

C) Education + Hand Hygiene + Face Masks

 

"Hand hygiene with or without facemasks seemed to reduce influenza transmission, but the differences compared with the control group were not significant." (Cowling et al 2009)

 

"No significant difference was found between the face-mask plus hand hygiene group and the hand hygiene group in RT-PCR–confirmed influenza virus infections in house-hold contacts." (Cowling et al 2009)

 

Significance

"No significant differences between surgical masks and control" (Cowling et al 2010 describing his own Cowling et al 2008 study)

 

"No significant difference overall" (Cowling et al 2010 describing his own Cowling et al 2009 study)

 

Found no statistically significant benefit from use of facemasks to control respiratory viral illnesses.

 

Full Citations

Cowling, Benjamin J., Rita O. P. Fung, Calvin K. Y. Cheng, Vicky J. Fang, Kwok Hung Chan, Wing Hong Seto, Raymond Yung, Billy Chiu, Paco Lee, Timothy M. Uyeki, Peter M. Houck, J. S. Malik Peiris, and Gabriel M. Leung. "Preliminary Findings of a Randomized Trial of Non-Pharmaceutical Interventions to Prevent Influenza Transmission in Households." PLoS One 3, no. 5 (2008): e2101.

https://dx.doi.org/10.1371/journal.pone.0002101

 

Cowling, B. J., K. H. Chan, V. J. Fang, C. K. Cheng, R. O. Fung, W. Wai, J. Sin, W. H. Seto, R. Yung, D. W. Chu, B. C. Chiu, P. W. Lee, M. C. Chiu, H. C. Lee, T. M. Uyeki, P. M. Houck, J. S. Peiris, and G. M. Leung. "Facemasks and Hand Hygiene to Prevent Influenza Transmission in Households: A Cluster Randomized Trial." Ann Intern Med 151, no. 7 (Oct 6 2009): 437-46. https://dx.doi.org/10.7326/0003-4819-151-7-

200910060-00142

 

Cowling, B. J., Y. Zhou, D. K. Ip, G. M. Leung, and A. E. Aiello. "Face Masks to Prevent Transmission of Influenza Virus: A Systematic Review." Epidemiol Infect 138, no. 4 (Apr 2010): 449-56.

https://dx.doi.org/10.1017/s0950268809991658

 

Reference 10

Author

Chin et al 2020

 

Type and Details

  • In vitro study of SARS-CoV-2 surface viability

  • Compares the length of time SARS-CoV-2

  • remains infectious on various surface materials.

 

Results and Quotes

Compared paper, tissue paper, wood, cloth, glass, banknotes, stainless steel, plastic, mask inner layer, and mask outer layer.

 

Of all the materials tested, SARS-CoV-2 remained viable longest on medical masks.

 

"No infectious virus could be recovered from printing and tissue papers after a 3-hour incubation, whereas no infectious virus could be detected from treated wood and cloth on day 2. By contrast, SARS-CoV-2 was more stable on smooth surfaces. No infectious virus could be detected from treated smooth surfaces on day 4 (glass and banknote) or day 7 (stainless steel and plastic). Strikingly, a detectable level of infectious virus could still be present on the outer layer of a surgical mask on day 7."

 

Significance

Findings show that SARS-CoV-2 remains viable longer on the inner and outer layer of medical masks than on most other common materials. Taken in conjunction with the inferior protective performance from other respiratory viruses of cloth masks, and the studies suggesting that medical masks and N95 masks have comparable performance, this suggests that the vast majority of masks in use today are not useful in preventing the spread of SARS-CoV-2, and may even have a detrimental effect by extending the

viral period of viability.

 

Full Citations

Chin, A. W. H., J. T. S. Chu, M. R. A. Perera, K. P. Y. Hui, H. L. Yen, M. C. W. Chan, M. Peiris, and L. L. M. Poon. "Stability of Sars-Cov-2 in Different Environmental Conditions." Lancet Microbe 1, no. 1 (May 2020): e10. https://dx.doi.org/10.1016/s2666-5247(20)30003-3

 

Reference 11

Authors

Gund et al 2020

Zhiqing et al 2018

Type and Details

  • In vivo observational study

  • Laboratory cultures of personal protective equipment used during patient procedures compared with unused PPE.

 

Results and Quotes

"The surgical mask seems to provide excellent conditions for the survival of oral or dermal bacteria."

 

"It was found that when wearing surgical masks for more than 2 h, an increasing number of microorganisms from the environment or from the oral cavity and respiratory system of the mask wearer accumulate."

 

"Touching the outer surface of the mask should be avoided at any time. After touching or removing the mask, the hands must be disinfected."

 

Significance

This study highlights several of the inescapable risk tradeoffs inherent in wearing masks.

 

Results indicate that a medical mask itself can be a source of pathogen contamination and transfer for both the user and those around them via transfer to the hands and other surfaces.

 

This has even stronger implications when taken in conjunction comparing the observed infection rates between cloth masks and medical masks in randomized controlled trials.

 

Even if effective in filtering viruses, masks (especially when worn beyond two hours) are known to provide excellent breeding grounds for bacteria, effectively trading a guaranteed dramatic increase in exposure to one pathogen for an unlikely protective benefit from another.

 

Full Citations

Gund, M., J. Isack, M. Hannig, S. Thieme-Ruffing, B. Gärtner, G. Boros, and S. Rupf. "Contamination of Surgical Mask During Aerosol-Producing Dental Treatments." Clin Oral Investig (Oct 27 2020): 1-8. https://dx.doi.org/10.1007/s00784-020-03645-2

 

Zhiqing, L., C. Yongyun, C. Wenxiang, Y. Mengning, M. Yuanqing, Z. Zhenan, W. Haishan, Z. Jie, D. Kerong, L. Huiwu, L. Fengxiang, and Z. Zanjing. "Surgical Masks as Source of Bacterial Contamination During Operative Procedures." J Orthop Translat 14 (Jul 2018): 57-62.

https://dx.doi.org/10.1016/j.jot.2018.06.002

Reference 12

Author

Kellogg 1920

 

Type and Details

  • Retrospective assessment and laboratory tests using humans to disperse proxy organisms.

 

Results and Quotes

The authors of this study used a proxy organism (Bacillus prodigiosus, also known as Serratia marcescens) which are typically 500 to 2,000 nanometers – many times the size of the 60-140nm SARS-CoV-2 virus.

 

"We found that with the element of aspiration introduced, as in the natural use of masks, even five layers did not give a sufficient reduction in count to make such a mask of value."

 

Significance

The author's stated intent was to seek an explanation for the utter lack of observed efficacy of facemasking during the Spanish Flu. "...masks, contrary to expectation, were worn cheerfully and universally, and also, contrary to expectation of what should follow under such circumstances, no effect on the epidemic curve was to be seen."

 

If cloth masks can't provide protection against an organism hundreds of times the size of a virus like SARS-CoV-2, they cannot reasonably be expected to protect against a virus either.

 

Full Citations

Kellogg, W. H., and Grace Macmillan. "An Experimental Study of the Efficacy of Gauze Face Masks." American Journal of Public Health 10, no. 1 (1920): 34-42. https://dx.doi.org/10.2105/ajph.10.1.34

 

Reference 13

Author

Laslett et al 1989

 

Type and Details

  • Prospective Review

  • Analyzed 504 operations involving 1008 operator-experiences total.

 

Results and Quotes

"Wearing of Caps and Masks Not Necessary During Cardiac Catheterization"

 

"... we found by a prospective review of the experience in our institution’s catheterization laboratory that whether caps or masks were worn by the operators performing the (percutaneous) procedures had no effect on the apparent infection rate."

 

Significance

The authors found no difference in the rate of post-operative infections for cardiac catherization procedures whether or not the surgeons wore caps and masks.

 

Full Citations

Laslett, Lawrence J., and Alisa Sabin. "Wearing of Caps and Masks Not Necessary During Cardiac Catheterization." https://doi.org/10.1002/ccd.1810170306, Catheterization and Cardiovascular Diagnosis 17, no. 3 (1989/07/01 1989): 158-60. Accessed 2021/04/07. https://dx.doi.org/https://doi.org/10.1002/ccd.1810170306

 

Reference 14

Authors

Smith et al 2016

Offeddu et al 2017

Long et al 2020

Bartoszko et al 2020

 

Type and Details

  • Meta-analyses

  • Incorporated randomized controlled trials and observational studies.

 

Results and Quotes

"Evidence of a protective effect of masks or respirators against VRI [viral respiratory infections, a rarer outcome, was not statistically significant." (Offeddu et al 2017)

 

"Disposable, cotton, or paper masks are not recommended." (Offeddu et al 2017)

 

"Single-use medical masks are preferable to cloth masks, for which there is no evidence of protection and which might facilitate transmission of pathogens when used repeatedly without adequate sterilization." (Offeddu et al 2017)

 

"There were no statistically significant differences in preventing laboratory-confirmed influenza, laboratory-confirmed respiratory viral infections, laboratory confirmed respiratory infection and influenzalike illness using N95 respirators and surgical masks." (Long et al 2020)

 

"The use of N95 respirators compared with surgical masks is not associated with a lower risk of laboratory-confirmed influenza." (Long et al 2020)

 

"There is no convincing evidence that medical masks are inferior to N95 respirators for protecting healthcare workers against laboratory-confirmed viral respiratory infections during routine care and non–aerosol-generating procedures." (Bartoszko et al 2020)

 

Significance

N95 masks have a filtration efficacy exceeding that of medical masks. When properly fitted, they are supposed to filter out 95% of particles greater than 300 nanometers in size. This filtration efficacy declines dramatically for particles <300nm, and respiratory viruses like SARS-CoV-2 and influenza are typically <150nm in diameter.  Nevertheless, laboratory studies have shown N95 masks to have superior filtration of <300nm particles when compared to medical masks.

 

The fact that multiple meta-analyses have consistently failed to demonstrate that N95 masks provide statistically significant real-world respiratory viral protection over medical masks despite laboratory studies arguing for their efficacy suggests that the same lack of additional benefit may very well be true when comparing surgical masks with no masks.

 

Full Citations

Smith, J. D., C. C. MacDougall, J. Johnstone, R. A. Copes, B. Schwartz, and G. E. Garber. "Effectiveness of N95 Respirators Versus Surgical Masks in Protecting Health Care Workers from Acute Respiratory Infection: A Systematic Review and Meta-Analysis." Cmaj 188, no. 8 (May 17 2016): 567-74. https://dx.doi.org/10.1503/cmaj.150835

 

Offeddu, V., C. F. Yung, M. S. F. Low, and C. C. Tam. "Effectiveness of Masks and Respirators against Respiratory Infections in Healthcare Workers: A Systematic Review and Meta-Analysis." Clin Infect Dis 65, no. 11 (Nov 13 2017): 1934-42.  https://dx.doi.org/10.1093/cid/cix681

 

Long, Y., T. Hu, L. Liu, R. Chen, Q. Guo, L. Yang, Y. Cheng, J. Huang, and L. Du. "Effectiveness of N95 Respirators Versus Surgical Masks against Influenza: A Systematic Review and Meta-Analysis." J Evid Based Med 13, no. 2 (May 2020): 93-101.  https://dx.doi.org/10.1111/jebm.12381

 

Bartoszko, J. J., M. A. M. Farooqi, W. Alhazzani, and M. Loeb. "Medical Masks Vs N95 Respirators for Preventing Covid-19 in Healthcare Workers: A Systematic Review and Meta-Analysis of Randomized Trials." Influenza Other Respir Viruses 14, no. 4 (Jul 2020): 365-73.  https://dx.doi.org/10.1111/irv.12745

 

Reference 15

Author

Mitchell et al 1991

 

Type and Details

  • In vivo simulation

  • In vivo simulation conducted in an operating room with unmasked volunteers breathing and speaking with their mouths and nostrils 15 cm (6 inches) from agar plates, and 1 meter from agar plates

 

Results and Quotes

"Oral microbial dispersal by talking non-scrubbed staff poses no risk to the patient on the operating table. The routine wearing of masks by all staff working in a modern operating room with forced ventilation is a costly and unnecessary ritual."

 

Significance

Outdoor conditions are even less conducive to microbial transmission than the operating room conditions in this study.

 

Wearing masks outdoors is utterly useless.

 

If masks don't provide protection against much larger bacteria, there is no reason to think they will be of any use against viruses.

 

These findings also imply that singing is not nearly as risky as many people now believe.

 

Full Citations

Mitchell, N. J., and S. Hunt. "Surgical Face Masks in Modern Operating Rooms--a Costly and Unnecessary Ritual?", J Hosp Infect 18, no. 3 (Jul 1991): 239-42. https://dx.doi.org/10.1016/0195-6701(91)90148-2

 

Reference 16

Author

Simmerman et al 2011

 

Type and Details

  • Cluster-Randomized Controlled Trial

  • Examined the rates of influenza transmission in households from symptomatic child index cases in Thailand.

  • Involved a total of 442 index children and 1,147 household members.

 

Results and Quotes

Secondary Influenza Attack Rates between the handwashing and handwashing + facemask group were identical.

 

"Influenza transmission was not reduced by interventions to promote hand washing and face mask use."

 

"Relative to the control group, the ORs [odds ratios] for ILI [influenza-like illness] among household members in the hand-washing arm (2Æ09; 95% CI 1Æ25, 3Æ50; P = 0Æ005) and hand washing plus face mask arm (2Æ15; 95% CI: 1Æ27, 3Æ62; P = 0Æ004) were twofold in the opposite direction from the hypothesized protective effect."

 

Significance

No differences in rates of upper respiratory infections between medical masks plus handwashing versus handwashing alone in risk for infections in household contacts of index cases STRONGLY implies that medical masks are not effective at preventing respiratory infections.

 

Full Citations

Simmerman, James M., Piyarat Suntarattiwong, Jens Levy, Richard G. Jarman, Suchada Kaewchana, Robert V. Gibbons, Ben J. Cowling, Wiwan Sanasuttipun, Susan A. Maloney, Timothy M. Uyeki, Laurie Kamimoto, and Tawee Chotipitayasunondh. "Findings from a Household Randomized Controlled Trial of Hand Washing and Face Masks to Reduce Influenza Transmission in Bangkok, Thailand."  Influenza and Other Respiratory Viruses 5, no. 4 (2011): 256-67. https://dx.doi.org/10.1111/j.1750-2659.2011.00205.x

Free people.png