Curated by Jeremy Howard and the fast.ai community. Summaries by Reshama Shaikh. Additional help from Frederik Questier. The papers below have been used to create a video, and a newspaper article, summarizing the utility of basic masks. In summary: everyone should wear masks, which they should make themselves using t-shirts and/or paper towels, whenever they go out in public. I’ve also made a little summary on Twitter of the video, and a summary of the article.
We ended up, somewhat accidentally, finding that we’d created a campaign after we made this literature summary! So now you’ll find lots of information about masks, including how to make your own, at Masks4All.co.
See next section for “summary of publications”
Lead Author / Year /
“moderate‐certainty evidence shows that use of handwashing plus masks probably reduces the spread of respiratory viruses”
Link 2 (2019)
-- a 50% compliance in donning the device resulted in a significant (at least 50% prevalence and 20% cumulative incidence) reduction in risk for fitted and unfitted N95 respirators, high‐filtration surgical masks, and both low‐filtration and high‐filtration pediatric masks.
--An 80% compliance rate essentially eliminated the influenza outbreak.
--Outward protection (mask wearing by a mechanical head) was less effective than inward protection (mask wearing by healthy volunteers)
Van der Sande / 2008 /
Experiment 1, n=28 adults + 11 children
Experiment 2, n=22 adults
Experiment 3, n= artificial test head
Mask: FF2, N95, homemade (tea cloth)
“overall these experiments show that significant protection against influenza transmission upon exposure can be conveyed also for lay people, including children, in spite of imperfect fit and imperfect adherence.”
none of those passengers in the two buses who wore face masks were infected.
-- homemade (cotton tshirts)
-- no mask
--surgical mask was 3 times more effective in blocking transmission than the homemade mask
--homemade mask should only be considered as a last resort to prevent droplet transmission from infected individuals, but it would be better than no protection.
(CDC / FAA)
p = 0.003
-- no mask
--11% vs 43% efficacy of masks (no mask vs mask)
van Doremalen /
“aerosol and fomite transmission of SARS-CoV-2 is plausible, since the virus can remain viable and infectious in aerosols for hours and on surfaces up to days”
--DO NOT use alcohol and chlorine-based disinfection methods.These will remove
the static charge in the microfibers in N95 facial masks, reducing filtration efficiency. In addition, chlorine also retains gas after de-contamination and these fumes may be harmful.
"As evidence suggests COVID-19 could be transmitted before symptom onset, community transmission might be reduced if everyone, including people who have been infected but are asymptomatic and contagious, wear face masks."
--This systematic review and meta-analysis supports the use of respiratory protection.
--However, the existing evidence is sparse and findings are inconsistent within and across studies
“wearing simple masks was highly effective ([odds ratios] 0.32, 0.25 to 0.40; five studies), wearing N95 masks was even more effective (0.09, 0.03 to 0.30; two studies)”
“The following effective interventions should be implemented, preferably in a combined fashion, to reduce transmission of viral respiratory disease:
--67 studies including randomised controlled trials and observational studies with a mixed risk of bias.
--Simple and low‐cost interventions would be useful for reducing transmission of epidemic respiratory viruses. Routine long‐term implementation of some measures assessed might be difficult without the threat of an epidemic.
--The use of N95 respirators compared with surgical masks is not associated with a lower risk of laboratory-confirmed influenza. --It suggests that N95 respirators should not be recommended for general public and non-high-risk medical staff those are not in close contact with influenza patients or suspected patients
--, the sensitivity analysis after excluding the trial by Loeb et al18 showed a significant effect of N95 respirators on preventing respiratory viral infections (RR=0.61, 95% CI 0.39-0.98, P < .05).
--WHO recommends protective equipment including masks (if they not available, a cloth to cover the mouth is recommended) for persons who must handle dead or ill chickens in regions affected by H5N1 (5).
-- Quality commercial masks are not always accessible, but anecdotal evidence has showed that handmade masks of cotton gauze were protective in military barracks and in healthcare workers during the Manchurian epidemic (6,7).
--simple, locally made, washable mask may be a solution if commercial masks are not available.
--Limit accidental droplet contamination of the hospital environment by implementing respiratory etiquette and by having everyone entering the facility (staff, patients, and visitors) use simple surgical masks. Assuming that resupply may be difficult during a pandemic, hospitals should stockpile enough masks for 3 weeks.
--Shortages of N95 masks should be anticipated,
--If no other masks are available, surgical masks, which will provide droplet protection, should be used.3 Powered air purifying respirators (PAPRs) should be available for use in high risk aerosol-generating procedures.
Understanding what we mean when we discuss airborne virus infection risk (Flight of the Aerosol)
For a virus described as spreading only through direct contact, recommendations for the use of masks, implying airborne spread to many, fuel such questions. In fact, face protection is recommended to prevent infectious droplets landing on vulnerable membranes (mouth and eyes).
--filtration performance of pleated hydrophobic membrane filters was demonstrated to be markedly greater than that of electrostatic filters
De Man /
The effectiveness of these processes are
sufficient to inactivate the coronavirus based on knowledge of inactivation of such viruses
--Clinical respiratory illness (CRI), --influenza-like illness (ILI) --respiratory virus infection
--Penetration of cloth masks by particles was almost 97% and medical masks 44%.
--Moisture retention, reuse of cloth masks and poor filtration may result in increased risk of infection. Further research is needed to inform the widespread use of cloth masks globally.
Wherever the surgeon operates more
than 2-3 hours at a stretch, he/she should change their face mask every 1.5 to 2 hours
--study helps to establish that in developing countries, where resources could be a constraint for providing disposable face masks, the
fabric face masks can also be used equally effectively
if changed frequently ideally at around 90 minutes.
Radonovich / 2019 /
N95 respirators vs medical masks as worn by participants in this trial resulted in no significant difference in the incidence of laboratory-confirmed influenza.
(82, 69 and 67 HH contacts = 218)
Results suggest that household transmission of influenza can be reduced by the use of NPI, such as facemasks and intensified hand hygiene, when implemented early and used diligently. Concerns about acceptability and tolerability of the interventions should not be a reason against their recommendation.
n=407 vs n=794
Hand hygiene and facemasks seemed to prevent household transmission of influenza virus when implemented within 36 hours of index patient symptom onset. These findings suggest that nonpharmaceutical interventions are important for mitigation of pandemic and interpandemic influenza.
“These findings suggest that face masks and hand hygiene may reduce respiratory illnesses in shared living settings and mitigate the impact of the influenza A(H1N1) pandemic.”
Review considered 126 studies and withheld 12 randomised controlled trials or reviews
“Systematic review evidence provides cautious support for the use of standard surgical masks in non AGPs [aerosol-generating procedures], though the empirical studies underpinning this conclusion were not in a COVID-19 population, and only one was in a community setting.”
“recommending surgical or procedural masks be worn by patients with suspected influenza to limit viral dissemination to others. “
2019-novel coronavirus (COVID-19)
“the protective role of both N95 and medical masks in other diseases could be translated into the fight against COVID-19, with specific contribution yet to be quantified”
n=493 medical staff
“infection rate for medical staff was significantly increased in the no-mask group compared with the N95 respirator group”
-- none of the 278 staff in the N95 group became infected, but 10 of 213 staff from the no-mask group were confirmed as infected
“WHO recommends against wearing masks in community settings because of lack of evidence. However, absence of evidence of effectiveness should not be equated to evidence of ineffectiveness, especially when facing a novel situation with limited alternative options. It has long been recommended that for respiratory infections like influenza, affected patients should wear masks to limit droplet spread. If everyone puts on a mask in public places, it would help to remove stigmatisation that has hitherto discouraged masking of symptomatic patients in many places. Furthermore, transmission from asymptomatic infected individuals has been documented for COVID-19, and viral load is particularly high at early disease stage. Masking, as a public health intervention, would probably intercept the transmission link and prevent these apparently healthy infectious sources.”
“the practices of Chinese residents were
very cautious: nearly all avoided crowded places
(96.4%) and wore masks when leaving the home
(98.0%) during the rapid rise period of the COVID-19
“For individuals, protective measures, including improving personal hygiene, wearing medical masks, adequate rest, and keeping rooms well ventilated, can effectively prevent SARS‐CoV‐2 infection.”
“The viral load that was detected in the asymptomatic patient was similar to that in the symptomatic patients, which suggests the transmission potential of asymptomatic or minimally symptomatic patients. These findings are in concordance with reports that transmission may occur early in the course of infection5 and suggest that case detection and isolation may require strategies different from those required for the control of SARS-CoV”
n = 9 cases, 32 controls
“Wearing a face mask was associated with a decreased risk for influenza acquisition during this long-duration flight.”
0% of mask-wearers got sick, but 35% of non-wearers did
“Face masks and hand hygiene combined may reduce the rate of ILI [influenza-like illness] and confirmed influenza in community settings. These non-pharmaceutical measures should be recommended in crowded settings at the start of an influenza pandemic.”
“Our study demonstrated a significant association between the combined use of face masks and hand hygiene and a substantially reduced incidence of ILI [influenza-like illness] during a seasonal influenza outbreak. If masks and hand hygiene have similar impacts on primary incidence of infection with other seasonal and pandemic strains, particularly in crowded, community settings, then transmission of viruses between persons may be significantly decreased by these interventions.”
“frequent mask use in public venues, frequent hand washing, and disinfecting the living quarters were significant protective factors (OR 0.36 to 0.58)”
“We now have some empirical evidence to suggest that wearing a face-mask frequently in public places, frequent handwashing, and disinfecting one's living quarter were effective public health measures to reduce the risk for transmission (adjusted OR 0.58 to 0.36).”
”members of the case group [infected with SARS] were less likely than members of the control group [not infected] to have frequently worn a face mask in public venues (27.9% vs. 58.7%, OR = 0.36, p < 0.005)” This effect was larger than that of frequent handwashing.
The N95 filtering face piece respirators may not provide the expected protection level against small virions. Some surgical masks may let a significant fraction of airborne viruses penetrate through their filters, providing very low protection against aerosolized infectious agents in the size range of 10 to 80 nm. It should be noted that the surgical masks are primarily designed to protect the environment from the wearer, whereas the respirators are supposed to protect the wearer from the environment.
the most important aspect of a NIOSH-certified respirator’s performance will be how well it fits to the face and minimizes the degree of leakage around the facepiece. This must be measured for each individual and their selected respirator. Selecting the right respirator for a particular workplace exposure depends largely on selecting the right level of protection.
N95 respirators were found to have higher filtration efficiencies than DM (dust/mist) and DFM (dust/fume/mist) respirators and noncertified surgical masks. Thus, N95 respirators provide excellent protection against airborne particles when there is a good face seal.
Breathing intensity and facial dimensions showed some (although limited) influence. Because most of the penetrated particles entered through the faceseal, the priority in respirator/mask development should be shifted from improving the efficiency of the filter medium to establishing a better fit that would eliminate or minimize faceseal leakage.
Consumer Council /
It is scientifically proved that DIY face mask with one facial tissue (inner layer on the face) and two kitchen paper towels as the outer layer achieved over 90% function of surgical mask in terms of filtration of 20-200nm aerosol. The Taskforce recommends that the public can consider using the above materials to make DIY face mask in time of acute shortage of surgical mask.
Transocular transmission of LAIV occured in most participants suggesting the necessity of eye protection. An N95 respirator provided the best guard further enhanced by eye protection.
Recent work has demonstrated that exhalations, sneezes, and coughs not only consist of mucosalivary droplets following short-range semiballistic emission trajectories but, importantly, are primarily made of a multiphase turbulent gas (a puff) cloud that entrains ambient air and traps and carries within it clusters of droplets with a continuum of droplet sizes
(Stanford & MIT research on droplet spread when speaking; includes message from Nobel Prize winning virologist, Harold Varmus) (stoptheviruscovid19.github.io)
Larson, 2010, USA
n=509 primarily Hispanic households
“Mask wearing is a promising non-pharmaceutical intervention to reduce risk of secondary transmission of viral URI [upper respiratory infections], but it is likely that adherence to mask wearing would occur only if there was a major pandemic that resulted in a heightened level of community concern and fear.”
“In this population, there was no detectable additional benefit of hand sanitizer or face masks over targeted education on overall rates of URIs, but mask wearing was associated with reduced secondary transmission and should be encouraged during outbreak situations.”
Leung, 2020, Hong Kong
Our results indicate that surgical face masks could prevent transmission of human coronaviruses and influenza viruses from symptomatic individuals.
Nishiura, 2020, Japan
Reduction of unnecessary close contact in closed environments may help prevent large case clusters and superspreading events.
MacIntyre, 2008, Australia
“Conclusions: This is the first RCT on mask use to be conducted and provides data to inform pandemic planning. We found compliance to be low, but compliance is affected by perception of risk. In a pandemic, we would expect compliance to improve. In compliant users, masks were highly efficacious. A larger study is required to enumerate the difference in efficacy (if any) between surgical and non-fit tested P2 masks.”
Abaluck, 2020, USA
“We recommend the immediate universal adoption of cloth facemasks, including homemade, and accompanying policies to increase the supply of medical masks for health workers. Universal adoption will likely slow the spread of the COVID-19 virus by reducing transmission from asymptomatic individuals. We provide strongly suggestive evidence from cross-country data that facemask use slows the growth rate of cases and deaths. This complements extant scientific data on mask usage. Our analysis suggests each cloth facemask generates thousands of dollars in value from reduced mortality risk. Each medical mask, when used by a healthcare worker, may generate millions of dollars in value, and policies to encourage greater production prioritized for health workers are urgently needed.”
About COVID-19: “The average daily growth rate of confirmed positives is 18% in countries with no pre-existing mask norms and 10% in countries with such norms.”
Zhang / 2020
Our estimates of the incubation period and serial interval were similar, suggesting an early peak of infectiousness, with possible transmission before the onset of symptoms. Our results also indicate that, as the epidemic progressed, infectious individuals were isolated more quickly, thus shortening the window of transmission in the community. Overall, our findings indicate that strict containment measures, movement restrictions, and increased awareness of the population might have contributed to interrupt local transmission of SARS-CoV-2 outside Hubei province.
Leffler / 2020
A recent review of the trajectory of per-capita mortality from COVID-19 infection in various countries demonstrated that mortality tends to approach an asymptote ranging between approximately 1 in 1,000,000 of the population in numerous countries which have advocated use of masks by the public, to approximately 1 in 3,200 killed in the hardest-hit countries, which have not advocated widespread use of masks. It is likely that many countries in the lowest-mortality group, which have advocated mask-wearing by the public, have been able to prevent well over 99% of their population from becoming infected. On April 4, 2020, the data related to Western countries, such as the Czech Republic, which recently mandated mask usage are consistent with a leveling-off of mortality. The authors recommended that all members of the public to wear a mask (or available face covering) whenever near other members of the public, or near surfaces touched by other members of the public (such as groceries, keyboards, tables, or doorknobs).
Fuk-Woo Chan / 2020
“Professor Yuen Kwok-yung, the University of Hong Kong’s (HKU) top microbiologist and an early proponent of wearing masks in the city, has described the case of a seven-year-old girl who resisted Covid-19 while her family members fell sick.
In a study published in the medical journal The Lancet, he said the family of six travelled to Wuhan, the epicentre of China’s Covid-19 outbreak, and the girl was the only one in the family who did not contract the virus. The reason: she wore masks throughout their trip.” (From: https://www.scmp.com/news/hong-kong/health-environment/article/3078437/mask-or-not-mask-who-makes-u-turn-while-us )
During January 26–February 10, 2020, an outbreak of 2019 novel coronavirus disease in an air-conditioned restaurant in Guangzhou, China, involved 3 family clusters. The airflow direction was consistent with droplet transmission
Anfinrud/Bax; medRxiv 2020)
Speaking may be a primary mode of transmission of SARS-CoV-2.