References

Hendrix, M., Walde, C., Findley, K., & Trotman, R. (2020). 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 2020MMWR. Morbidity And Mortality Weekly Report, 69(28), 930-932.(July 14 2020)  https://doi.org/10.15585/mmwr.mm6928e2 CASE STUDY. 

  • Two hairstylists in Springfield, Missouri developed COVID-19 symptoms. They both worked in a busy hair salon, masked before being diagnosed, after displaying symptoms—139 clients and workers were exposed, and 48.2% of them were later tested. All tested negative. This case study, though, had some limitations. Half of the exposed clients refused to be tested, and it’s unknown if the clients had any other health conditions (many were seniors). Most significantly, viral shedding is highest 2-3 days before symptoms appear, and none of the clients recruited for the study were present during this period. A hairstylist also faces the back of their clients’ heads, which may limit transmission.

Howard, J., Huang, A., Li, Z., Tufekci, Z., Zdimal, V., & van der Westhuizen, H. et al. (2020). Face Masks Against COVID-19: An Evidence Review. (April 12 2020) https://doi.org/10.20944/preprints202004.0203.v1 PREPRINT LITERATURE REVIEW.  

  • This literature review focused on filtering efficiency of masks, population impacts of mask-wearing, and policy implications. It is an attempt to examine the impact of source control (preventing the wearer from spreading droplets). Mask studies likely underestimate mask effectiveness, as droplets—which are larger—is what is primarily expressed by humans. Masks create a barrier that prevent droplets from becoming aerosols. Any kind of mask will substantially prevent droplets from becoming aerosolized, but homemade cloth masks filter 49-86% of particles, and surgical masks filter 89% of particles the same size. One study,  which didn’t look at COVID-19,  found masks were effective at blocking coronavirus droplets. It likely works on COVID-19 but not rhinovirus or flu. Surgical masks are three times more effective at blocking transmission from another person. One study found surgical masks were more effective for healthcare workers (likely due to them being clean). This  does not necessarily translate to a community setting. It may be the case that mask-wearing reinforces the seriousness of public health efforts and encourages compliance in other areas. 

Fischer, E., Fischer, M., Grass, D., Henrion, I., Warren, W., & Westman, E. (2020). Low-cost measurement of face mask efficacy for filtering expelled droplets during speech. Science Advances, 6(36), eabd3083. (Sept 2, 2020)  https://doi.org/10.1126/sciadv.abd3083 RANDOMIZED CONTROL TRIAL. 

  • This RCT tested 14 types of face coverings in a lab setting. Subjects spoke into a laser beam, and their expressed droplets scatter light, which was measured by a camera. This had the advantage of eliminating noise in the data, as the same person spoke the same words at the same intensity in the same environment. The downside was in the real world, differences in physiology, speech pattern, etc. might affect the results. Not everyone speaks or moves the same, or has the same mouth shape. The most effective was the N95, followed by the  surgical paper mask, poly/cotton two layer, two layer poly, poly mask. The least effective was the neck gaiter, which performed worse than nothing (control),  then bandana, knitted, two-layer cotton pleated, 1-layer cotton pleated. Possible limitations may be that the laser and algorithm might not be accurate, as this experimental method has not been tried before. Some droplets might transfer through the mask and not be seen by the laser, as a cell camera might not be high enough resolution.

Lindsley, W., Blachere, F., Law, B., Beezhold, D., & Noti, J. (2020). Efficacy of face masks, neck gaiters and face shields for reducing the expulsion of simulated cough-generated aerosolsdoi: 10.1101/2020.10.05.20207241 (Nov. 16, 2020) RANDOMIZED CONTROL TRIAL

  • An RCT using a cough aerosol simulator to propel particles up to 7 µm to different masks and face coverings. Different masks were placed on a standard head form. The N95 blocked 95% of aerosol, the double-layer gaiter 60%, the cloth face mask 51%, the single layer gaiter 47%, and the face shield 2%. The small particles studied are less likely to fall close to the source, but to spread. Small particles can remain airborne for hours, and thus it’s critical that they’re blocked by a mask or covering. Limitations on this study are that they used a cough simulator and not actual people, and the uniform head form doesn’t reflect the diversity of actual head and face shapes. They studied coughing but not breathing or speaking, and only one sample of each kind of mask, gaiter, or shield. In addition, proper usage and hygiene (eg cleaning masks) would affect particulate spread. The cough simulator was a modified version of one used in previous experiments. 
Bahl, P., Bhattacharjee, S., de Silva, C., Chughtai, A., Doolan, C., & MacIntyre, C. (2020). Face coverings and mask to minimize droplet dispersion and aerosolization: a video case study. Thorax, thoraxjnl-2020-215748.(July 9 2020) https://doi.org/10.1136/thoraxjnl-2020-215748. CASE STUDY.
  • A video case study (which is not ideal as it’s a case study in controlled conditions) compared one-layer (cotton shirt) vs. two-layer (the sew method prescribed by the CDC) vs. a three-layer surgical mask and then used a high-speed camera and LED lighting to study the pattern of aerosol and droplets. From least to most effective, the options were no mask, one-layer, two-layer, and three-layer surgical, although many other factors go into determining mask efficacy. One study found a 12-layer cotton mask was as effective as a surgical mask. Any guidelines on homemade masks should stipulate a minimum of three layers. 
Leung, N., Chu, D., Shiu, E., Chan, K., McDevitt, J., & Hau, B. et al. (2020). Respiratory virus shedding in exhaled breath and efficacy of face masksNature Medicine, 26(5), 676-680. doi: 10.1038/s41591-020-0843-2 RANDOMIZED CONTROL TRIAL
  • Looking at seasonal coronaviruses, flu viruses, and rhinoviruses that are exhaled by the coughs and breath of infected people, researchers screened 246 individuals in two study phases who provided exhaled breath samples. Half of them didn’t wear a mask. Researchers tested for viral shedding with nasal swabs and throat swabs and compared the masked group vs. the maskless group.

Anfinrud, P., Stadnytskyi, V., Bax, C. and Bax, A., 2020. Visualizing Speech-Generated Oral Fluid Droplets with Laser Light Scattering. New England Journal of Medicine, 382(21), pp.2061-2063. (May 2020) LETTER CORRESPONDENCE

  • In a letter, a trio of researchers described how they used a laser, a light sheet, and a cardboard box to determine the number of droplets that were produced by a speaker who said the words “stay healthy.” Then a damp washcloth, acting as a mask, was placed over the mouth of the speaker to determine if there was a decrease in those droplets.
MacIntyre, C., Chughtai, A., Seale, H., Dwyer, D., & Quanyi, W. (2020). Human coronavirus data from four clinical trials of masks and respirators. International Journal Of Infectious Diseases, 96, 631-633. (May 26 2020 ) https://www.ijidonline.com/article/S1201-9712(20)30399-4/fulltext. RANDOMIZED CONTROL TRIAL
  • Four RCTs of coronavirus transmission, including one household, one healthcare, and two community RCTS. All had a small sample size. In one, children with influenza wore medical masks vs. a control group. One parent of an infected child in the control arm developed coronavirus, though none in the mask arm did. There is a lack of statistical significance, but researchers refer to a Hong Kong study showing that masks prevent transmission through breathing. In the source control trial, patients stopped wearing a mask when the symptoms ceased, and there was some degree of mask use reported in the control groups.
Xi, J.,  Xiuhua A., and Nagarajan, R. (2020). Effects of mask-wearing on the inhalability and deposition of airborne SARS-CoV-2 aerosols in human upper airway. Physics of Fluidshttps://aip.scitation.org/doi/10.1063/5.0034580 LAB STUDY
  • This study showed that surgical masks are 65% effective in filtering out particles from the air, but if a used mask is worn instead of a new one, that percentage drops tremendously. In fact, wearing a used and/or soiled mask might be even worse than not wearing a mask at all. That’s because a dirty three-layer mask can’t filter out as many particles as a brand new one.
Ho, K., Lin, L., Weng, S., & Chuang, K. (2020). Medical mask versus cotton mask for preventing respiratory droplet transmission in micro environments. Science Of The Total Environment, 735, 139510.(May 16 2020)  https://doi.org/10.1016/j.scitotenv.2020.139510. LAB STUDY
  • This was a panel study to determine whether cotton masks could suppress respiratory droplets as well as medical masks. The participants in this study mainly had influenza. Only six had confirmed COVID-19 cases. Participants wore medical and three-layer cotton masks under identical conditions in front of an air-conditioning unit in either a bedroom or a car. FFP-2 masks reduced droplets the most, followed by surgical, and then cloth masks. The cloth masks were made from T-shirts, which are thin. The study suggests cloth masks may be useful in normal environments if proper hygiene is practiced.
Drewnick, F., Pikmann, J., Fachinger, F., Moormann, L., Sprang, F., & Borrmann, S. (2020). Aerosol filtration efficiency of household materials for homemade face masks: Influence of material properties, particle size, particle electrical charge, face velocity, and leaks. Aerosol Science And Technology, 1-17. (August 28, 2020) https://www.tandfonline.com/doi/full/10.1080/02786826.2020.1817846 LAB STUDY
  • Filtration efficiency of various materials was measured against electrically-charged or neutral particles, spread by a diffuser. Particle sizes ranging from 30nm-10µm were examined. The materials were measured in isolation, not on a face or in normal usage, and 48 different fabric types were measured: natural, synthetic, and medical. Large particles were more likely to be filtered out than small ones. The synthetic fabrics were more efficient in filtering the small particles. Cotton and silk (natural fibers) were also efficient at filtering small particles. Filtration efficiency for neutrally-charged particles is low for small particles, except for FFP-2, surgical mask, vacuum cleaner bag, and linen case. The more layers and the tighter the weave resulted in the best efficiency. More flexible fabrics (fleece, terrycloth, felt) performed better than stiff materials (paper, coffee filter). Triangular bandage, terrycloth, vacuum bags, microfiber, felt, and velour performed better or as well as surgical masks. This study also attempted to account for gaps between the mask and the face, which inhibit filtration. They performed dedicated measurements with a surgical mask and velvet cotton. They attempted to replicate leaking via holes punched out of the sample. They find leaks inhibit barriers but cautioned this is qualitative. This paper achieved different findings than most regarding surgical vs cloth masks. The authors acknowledged this and attributed it to their measuring smaller particles. They agree with the majority of studies that more layers are better. Stacked and fluffy textile achieves the same filtration capacity as surgical masks for particles > 500mn. 
Zangmeister, C., Radney, J., Vicenzi, E., & Weaver, J. (2020). Filtration Efficiencies of Nanoscale Aerosol by Cloth Mask Materials Used to Slow the Spread of SARS-CoV-2ACS Nano, 14(7), 9188-9200. (June 25, 2020) doi: 10.1021/acsnano.0c05025 RANDOMIZED CONTROL TRIAL
  • This study took 32 materials that could be used in cloth masks and tested for filtration efficiency, differential pressure, quality factor, and construction parameters. The idea was to determine which kinds of cloth masks would be the most effective in stopping the spread of COVID-19. For this mask research, the authors tested 14 cotton, nine synthetic, four synthetic blends, four synthetic/cotton blends, and one wool sample. Surgical masks and N95 respirators were also tested. 
Wang, Y., Tian, H., Zhang, L., Zhang, M., Guo, D., & Wu, W. et al. (2020). Reduction of secondary transmission of SARS-CoV-2 in households by face mask use, disinfection and social distancing: a cohort study in Beijing, China. BMJ Global Health, 5(5), e002794. (May 11 2020) https://doi.org/10.1136/bmjgh-2020-002794. COHORT STUDY 
  • This paper focuses on risk reduction within families. It focused on people living with someone who had confirmed COVID-19. There were 399 confirmed cases in 181 families. It found face mask use in the household reduced transmission by 79%. This only applies if masks were worn before illness onset. It confirms transmission is highest prior to symptom onset. If found instances of fecal transmission, making this a unique circumstance as most mask studies to not account for this form of transmission. In addition, proper household cleaning protocols reduced transmission regardless of masks
Cheng, V., Wong, S., Chuang, V., So, S., Chen, J., & Sridhar, S. et al. (2020). The role of community-wide wearing of face mask for control of coronavirus disease 2019 (COVID-19) epidemic due to SARS-CoV-2. Journal Of Infection, 81(1), 107-114. (April 17) https://www.journalofinfection.com/article/S0163-4453(20)30235-8/fulltext OBSERVATIONAL STUDY
  • This paper compares Hong Kong to similar countries (in terms of population density, healthcare, and other health measures) where there were no community-wide masking. Hong Kong is unique in that masking in the community was more common before COVID-19, as a result of previous pandemics SARS and H1N1. This provides a way to isolate masking as a variable when compared to regions with similar populations, densities, and culture, such as Singapore. The study found a significant difference in infection rates between Hong Kong (961 confirmed cases, 53.8% imported)  and Singapore (1,481 confirmed, 38.3% imported), two cities that very similar except for mask usage. The paper acknowledges that the fact that there is no uniform directive on masking practices limits its utility. It may also be the case that the spread from masks is in large part because they prevent face touching.
Lyu, W., & Wehby, G. (2020). Community Use Of Face Masks And COVID-19: Evidence From A Natural Experiment Of State Mandates In The US. Health Affairs39(8), 1419-1425. (August) https://doi.org/10.1377/hlthaff.2020.00818 OBSERVATIONAL STUDY. 
  • This paper compared jurisdictions with masks to other jurisdictions without them. It used county-level data for 15 states plus Washington D.C., from Mar 25-May 2. Data based on public orders to wear masks (assuming these orders were followed to the same degree) found that case rate decreased by 2%, by 3 weeks after mask orders were imposed. Confounders include other measures such as distancing and hygiene, as well as different states having different measures and different rates of following orders. A predictive model estimates 230,000-450,000 infections were averted compared to if states did not impose mask orders, as the effectiveness of mask mandates increase the longer they are in place.

Walde, K. (2020). Face Masks Considerably Reduce COVID-19 Cases in Germany: A Synthetic Control Method Approach. Institute of Labor Economics (June) https://www.iza.org/publications/dp/13319/face-masks-considerably-reduce-covid-19-cases-in-germany-a-synthetic-control-method-approach. SYNTHETIC CONTROL METHOD.

  • Different cities in Germany were studied before and after masks were mandated in public, and this paper found that reported cases decreased after 10 days of masks being required. In the city of Jena, there were 25% fewer cumulative reported cases after 20 days. Jena introduced mandatory masks before other regions of Germany, and overall, there was a reduction between 2-13%. The effect was greatest in cities with high population density, and the greatest effect was found in on older populations, despite age being a risk factor. Possible explanations include greater compliance or these populations being less likely to go out. 

Karaivanov, Alexander; Shih En Lu, Hitoshi Shigeoka, Cong Chen, and Stephanie Pamplona (2020. Face Masks, Public Policies and Slowing the Spread of COVID-19: Evidence from Canada. National Bureau of Economic Research. Working Paper No. 27891(Oct 1 2020) https://www.nber.org/papers/w27891.  

  • This paper attempts to quantify the impact of mask mandates and other non-pharmaceutical interventions in Canada on the growth of cases. It compares rates in different provinces to gauge the effectiveness of interventions. It found within a few weeks of a mask mandate, known weekly cases were reduced between 25-46%. Data was collected between March and August, and used the Google COVID-19 community mobility reports, which in turn use smartphone geo-location. The data for each day of the week is compared for five weeks. In Ontario, the data on masked mandates and lagged case growth (14 days) suggests that mask mandates are effective. Universal indoor mask rules are more effective than those for employees only. Higher levels of confirmed cases correspond to lower case growth in the next cycle. However, this data is affected by other measures, such as hygiene, distancing, and staying home. It was found that mandates increase compliance for always wearing a mask in public by 30%. The authors emphasise this is not a substitute for RCTs. 

Gallaway, M., Rigler, J., Robinson, S., Herrick, K., Livar, E., & Komatsu, K. et al. (2020). Trends in COVID-19 Incidence After Implementation of Mitigation Measures — Arizona, January 22–August 7, 2020. Morbidity and Mortality Weekly Report. (October 6 2020) Morbidity And Mortality Weekly Report, 69(40). https://doi.org/10.15585/mmwr.mm6940e3

  • This is collected data concerning trends in Arizona after mitigation measures were implemented. It compares daily known cases and seven-day moving averages between January 22-August 7. The state issued and enforced many measures, including shelter in place orders, business and school closures, and mandatory masks at different times. Cases rose slightly as stay-home orders were lifted, and then spiked significantly as usual business resumed. Mask orders had an immediate, significant drop in reported cases, although the numbers rose again after two weeks. Case rates corresponded more closely to lockdown measures than masks. As this is a collection of data it has several limitations. There are many factors involved in mitigation; it is unknown if the measures represent correlation or causality. Other factors may be at play. There may be incomplete data for tribal territories. While mitigation measures were encouraged, actual adherence rates are unknown. There may also be factors unique to Arizona that makes it impractical to generalize to other regions. 

Van Dyke, M., Rogers, T., et al. (2020). Trends in County-Level COVID-19 Incidence in Counties With and Without a Mask Mandate—Kansas, June 1–August 23, 2020. CDC Morbidity and Mortality Weekly Report. (Nov. 20, 2020). CDC.gov. OBSERVATIONAL STUDY. 

  • The CDC collected findings on nearly three months worth of COVID-19 data in Kansas. After Kansas instituted a mask mandate in July, 81 out of the state’s 105 counties opted out of enforcing it. As this CDC Morbidity and Mortality Weekly Report noted, the 24 counties that actually enforced it saw a net decrease of 6% in COVID-19 incidence in the state’s seven-day rolling average. The counties that opted out saw an increase in 100% of coronavirus cases. 

Rader, B., White, L., Burns, M., Chen, J., Brilliant, J., & Cohen, J. et al. (2021). Mask-wearing and control of SARS-CoV-2 transmission in the USA: a cross-sectional study. The Lancet Digital Health. https://doi.org/10.1016/s2589-7500(20)30293-4 (Jan 2021) CROSS-SECTIONAL STUDY

  • More than 370,000 surveys were given in the summer of 2020 with questions about people’s mask-wearing habits when they were outside of the home. Those answers were compared to the public data on COVID-19, and researchers used models to determine the correlation between how many people wore masks and how much people were spreading the virus to one another in those communities.

Seegert, N., Gaulin, M., Yang, MJ., Navarro-Sanchez, F. (2020). Impact of Masks on Economic Activity. Marriner S. Eccles Institute For Economics and Quantitative Analysis. (Nov. 23, 2020). University of Utah. META ANALYSIS

  • This study from the University of Utah’s business school studied data that included consumer mobility via GPS on cell phones, credit card spending, and COVID-19 case numbers from all 3,142 U.S. counties and determined that promoting mask wearing decreases the number of COVID-19 cases while increasing consumer mobility and consumer spending. The study, which was still waiting to be peer-reviewed and published, also determined that statewide mask mandates were more effective than mandates in different counties.
Gandhi, M., Beyrer, C., Goosby, E.  (2020). Masks Do More Than Protect Others During COVID-19: Reducing the Inoculum of SARS-CoV-2 to Protect the Wearer. Journal of General Internal Medicine (July 31, 2020). https://link.springer.com/article/10.1007/s11606-020-06067-8 META ANALYSIS
  • This study shows that masks do more than protect you from the coronavirus. But it shows that if you were infected despite wearing a mask, that mask will still have benefitted you. If you end up contracting COVID-19, it’ll likely have less viral load, meaning you’d probably be either asymptomatic or have a mild case. Masks can help reduce the viral inoculum, another reason they could be so important. 

Chu, D., Akl, E., Duda, S., Solo, K., Yaacoub, S., & Schünemann, H. et al. (2020). 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. The Lancet, 395(10242), 1973-1987. (June 1 2020) https://doi.org/10.1016/s0140-6736(20)31142-9. SYSTEMATIC REVIEW

  • This review attempts to find the ideal distance, face, and eye protection for avoiding transmission. It includes observational and comparative studies but no RCTs, as those mainly pertain to the flu, not coronavirus or SARS. Sixty-six studies focused on how far the virus can travel, and of these, five looked at physical properties of the virus. The review did not use case studies or qualitative studies to measure effect. The studies found best evidence includes recommending two meters of physical distancing and wearing masks, although these only reduce, not eliminate, the risk. This review found that N95/FFP masks were more effective; this contradicts other studies where this finding is difficult to ascertain. They found evidence that face masks were protective for both healthcare professionals and the community. Unlike other papers, they found masks to be equally useful for both settings, once the unlikelihood of non-healthcare professionals wearing N95s was accounted for. There is slight evidence respirators are more protective than surgical masks. It is of greater importance that everyone wears a mask rather than the type of mask. This review does not include papers published after May 13. 
Esposito, S., Principi, N. (2020) To mask or not to mask children to overcome COVID-19. European Journal of Pediatrics. (May 9, 2020) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7210459/. META-ANALYSIS
  • The researchers came to the conclusion that universal mask-wearing is vital, and that includes children over the age of 2. That’s because, even though children were not thought to be major spreaders early in the pandemic, studies from Italy and China showed that children tend to be asymptomatic and can spread the virus to others. 
Jain, M., Kim, S., Xu, C., Li, H., & Rose, G. (2020). Efficacy and Use of Cloth Masks: A Scoping Review. Cureus. (Sept 13 2020) https://doi.org/10.7759/cureus.10423 LITERATURE REVIEW. 
  • This paper compares studies that examine the efficacy of cloth vs. surgical vs. N95 masks, although there is little data on this subject. One study found that 100% cotton masks were the best non-surgical mask, but this assumes COVID-19 particles are the same size as the 2002 SARS outbreak particles. There is likely no difference in compliance between cloth and surgical masks. Policymakers should focus on mask availability rather than material, in particular for community settings. While there is evidence cloth is less effective in health care settings, there is no evidence this is the case for community settings. Limitations include the lack of both community and laboratory data, particularly concerning the variety in materials and styles of cloth masks. This review also limited itself to published studies, which is a factor when this is a dynamic field of inquiry with plenty of gray literature. It may be difficult to find quality RCTs due to ethical considerations. The authors caution that homemade masks use such a variety of materials and fit, it’s hard to make generalizations.

MacIntyre, C., & Chughtai, A. (2020). A rapid systematic review of the efficacy of face masks and respirators against coronaviruses and other respiratory transmissible viruses for the community, healthcare workers and sick patients. International Journal Of Nursing Studies, 108, 103629. (April 21) https://doi.org/10.1016/j.ijnurstu.2020.103629 SYSTEMATIC REVIEW

  • This paper systematically reviews RCTs in community settings, home, and healthcare settings. In healthcare settings, respirators are more protective than surgical masks, which are more protective than cloth. Masks on sick patients are likely protective, and in the community, masks appeared to be effective with and without other hygiene methods, although it’s best when both are combined. Limitations are that some RCTs had no control arms or small sample sizes, and only one study examined COVID-19. COVID-19 particles were found only in exhalation of non-mask groups.

Boškoski, I., Gallo, C., Wallace, M., Costamagna, (2020) COVID-19 pandemic and personal protective equipment shortage: protective efficacy comparing masks and scientific methods for respirator reuse. Gastrointestinal Endoscopy.  https://www.sciencedirect.com/science/article/pii/S0016510720342474. LITERATURE REVIEW

  • Researchers showed that N95 masks should be limited to high-risk scenarios to help combat the shortage of PPE during the pandemic, because surgical masks “are not inferior compared with N95 respirators in terms of protective efficacy among healthcare workers.” Of the top 25 cited articles, 15 were used for this review. 

Perić, R., & Perić M. (2020) Analytical and Numerical Investigation of the Airflow in Face Masks used for Protection against COVID-19 Virus –Implications for Mask Design and Usage. Journal Of Applied Fluid Mechanics, 13(06). https://arxiv.org/abs/2005.08800 RCT

  • This study shows that previous research suggests that the design of most masks does not provide for reliable protection. The study’s authors used 2-D geometry and “commercial computational fluid dynamics software” to determine if exhaled droplets are allowed to escape the gaps between the mask and the mask-wearer’s face. According to the researchers, self-made masks and surgical masks do not provide enough protection. 

Matuschek, C., Moll, F., Fangerau, H., Fischer, J., Zänker, K., & van Griensven, M. et al. (2020). Face masks: benefits and risks during the COVID-19 crisis. European Journal Of Medical Research, 25(1). https://doi.org/10.1186/s40001-020-00430-5.

  • There is only weak evidence for wearing a face mask as an efficient hygienic tool to prevent the spread of a viral infection. However, the use of surgical masks seems to be linked to relevant protection during close contact scenarios by limiting pathogen-containing aerosol and liquid droplet dissemination.

Dugre, N. Masks for prevention of viral respiratory infections among health care workers and the public. Vol 66: July 2020 Canadian Family Physician. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7365162/ SYSTEMATIC REVIEW

  • This review found differences in studies concerning mask efficacy. One possible issue is mask use is correlated with other safety measures in the general population. It emphasizes the need for RCTs in order to have reliable information. Some experimental lab-based studies have found efficacy with wearing masks, but this does not always translate into a clinical setting. This review also separates studies using healthcare professionals vs. the general population. Surgical masks are likely more effective than cloth, but this was not statistically significant and found only in one study. N95 masks s are superior still. Ultimately, while it says there was little evidence that masks in the community setting reduces viral respiratory infections, they still found evidence masks reduces illnesses in those who wear them (unclear if correlation or causation). The clinical trials which showed masks had no effect were the ones which most closely reflected real-life settings, indicating poor mask practices might be a factor.
Bundgaard, H., Bundgaard, J., et al. (2020). Effectiveness of adding a mask recommendation to other public health measures to prevent SARS-CoV-2 infection in Danish mask wearers. Annals of Internal Medicine. (Nov. 18, 2020)  https://www.acpjournals.org/doi/10.7326/M20-6817#:~:text=Conclusion%3A,and%20uncommon%20general%20mask%20use RANDOMIZED CONTROL TRIAL
 
  • Participants in Denmark were assigned to the mask (disposable surgical) vs the control group in April and May of 2020. During the trial, other measures (such as distancing and hygiene) were implemented, so it’s difficult to say that mask usage was the deciding variable. The participants responded to an ad, were out of the home for at least three hours and did not wear masks at work. This already represents a niche within the populations. Researchers determined that mask recommendations to supplement other public health measures did not reduce the coronavirus infection rate among those who wore the masks by more than 50%.
Fischer, R., Morris, D., van Doremalen, N., Sarchette, S., Matson, M., & Bushmaker, T. et al. (2020). Effectiveness of N95 respirator decontamination and reuse against SARS-CoV-2 virus. Emerging Infectious Diseases, 26(9), 2253-2255. CDC.gov (September 2020)
  • Concerns N95 masks. Researchers wanted to see if they were still effective if they were contaminated and reused. Four methods of decontamination (UV, dry heat, ethanol, VHP). Filtration performance was measured after each decontamination and after two hours of wear. The first test showed there was no significant decrease in performance after the first decontamination, but degraded after each decontamination, in particular masks treated with ethanol and and heat. They recommend masks can be re-used up to three times assuming the fit and seal are unaffected.