Disposable face masks and reusable face coverings as ...

Best-published evidence supports the combined use of vaccines with non-pharmaceutical interventions (NPIs), to reduce the relative risk of contracting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes COVID-19; this will enable a safe transition to achieving herd immunity. Albeit complex, the strategic public health goal is to bundle NPIs to keep the basic reproduction number R 0 below one. However, validation of these NPIs is conducted using random clinical trials, which is challenging in a swiftly moving pandemic given the need for recruiting large participant cohort over a longitudinal analysis period. This review highlights emerging innovations for potentially improving the design, functionality and improved waste management of disposable face masks such as filtering facepiece (FFPs) respirators, medical masks, and reusable face coverings to help prevent COVID-19. It describes use of different mathematical models under varying scenarios to inform efficacy of single and combined use of NPIs as important counter-measures to break the cycle of COVID-19 infection including new SARS-CoV-2 variants. Demand for face masks during COVID-19 pandemic keeps increasing, especially for FFPs worn by medical workers. Collaborative and well-conducted randomised controlled trials across borders are required to generate robust data to inform common and consistent policies for COVID-19 and future pandemic planning and management; however, current use of systematic reviews of best available evidence can be considered to guide interim policies.

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Given the aforementioned, the purpose of this review is (1) to highlight key developments surrounding sustainable use of disposable face masks such as PPE, medical masks, and reusable face coverings; (2) to review the role of face masks in the context of other NPIs in breaking the cycle of COVID-19 infection, and; (3) to use relative risk assessment and statistical modelling to inform efficacy of single, and combined NPIs to prevent COVID-19 transmission with particular emphasis on different face mask designs and functionality features. This review does not address non-disposable filtering facepiece (FFP3) respirators.

'Face masks are physical barriers to respiratory droplets that may enter the mouth and nose and to the expulsion of mucosalivary droplets from infections individuals' ( Chua et al., ). The classification of, and technical standards for, different type of disposable masks available according to their intended use, as defined by the European Centre for Disease Prevention and Control () , has been comprehensively described by Rubio-Romero et al. () . In brief, (a) filtering facepiece (FFP) respirators are classified as PPE and are designed to protect the wearer from exposure to airborne contaminants, such as N95-type respirators; (b) medical face masks (also known as surgical or procedural masks), are classified as a medical device that covers the mouth, nose and chin ensuring a barrier that limits the transition of infective agent between hospital staff and patients; and (c) other face masks (also commonly known as non-medical, home-made cloth or barrier masks) includes various forms of self-made or commercial masks, or face coverings, made of cloth or textiles that are not standardized and not intended for use in healthcare settings ( Rubio-Romero et al., ) ( Fig. 1 ). The effectiveness of these disposable FFP masks is different depending on type and certification, which is established across 3 levels of protection depending on leakage of all particles into the interior, either through the adjustment of the mask to the face, by the exhalation valve, if any, or penetration through the filter that are 22%, 8% and 2% for FFP1, FFP2 and FFP3 respectively. The effectiveness of two types of medical masks, namely surgical or procedural masks, is defined by bacterial filtration efficiency, differential pressure (Pa/cm 2 ), splash resistant pressure (kPa) and microbial cleaning. Improvised non-medical face coverings are intended for low-risk cases where the risk of infection can be potentially increased due to humidity, liquid diffusion and virus retention ( European Centre for Disease Prevention and Control, b ).

The first COVID-19 vaccine, manufactured by Pfizer-BioNTech, was administered in the UK today ( Diaz, ). Priority emphasis has been placed on protecting the most vulnerable to reduce illness and death. While Phase 3 clinical trial data highlights both safety and 95% efficacy for this vaccine, it will take time to observe if it prevents COVID-19 transmission and creates broad herd immunity in communities. Thus, despite this positive news, there will remain a strong reliance on the combined use of NPIs to prevent COVID-19 transmission. The Republic of Ireland has managed to curtail two waves of COVID-19 through effective implementation of these NPIs, along with enforcing two lockdowns ( Government of Ireland, ); however, key challenges remain including greater mingling of people due to the opening up of hospitality that coincides with the festive Christmas holiday period. There is sustained pressure on maintaining supply chains of vital personal and protective equipment (PPE) to ensure that frontline healthcare workers, and the most at risk populations are protected ( Rowan and Laffey, b ; Cook, ; Flaxman et al. ; Perencevich et al., ).

Precisely how coronavirus spreads between susceptible individuals remains a matter of debate, but transmission of this respiratory virus may be through contact, droplet, or airborne spread ( Asadi et al. ). 'Direct' modes indicate person-to-person transmission such as via contaminated hands, or indirectly via fomites, which are inanimate or non-living objects or materials (i.e. transfer via a contaminated door handle through touch). If we touch a contaminated surface, we may then potentially transfer the virus onto the face mask if adjusting it, and may then directly inoculate the virus onto mucosal surfaces such as through the touching of the nose or eyes ( Wibisono et al., ). Droplet and airborne spread occur through the air through sneezing, coughing, singing, talking and exhaling ( Chua et al., ). It is appreciated that particles larger than 5 μm may fall to the ground within 1 m. However, a 'gas cloud' theory has been proposed where aggregated mucosalivary droplets from these different exhalation activities can form a cloud, and potentially be expelled up to 7 to 8 m in combination with environmental factors ( Bourouiba, : Dbouk and Drikakis, a , Dbouk and Drikakis, b ). Uncertainty surrounding the modes by which these respiratory viruses transmit among humans under varying conditions hinders evaluation of the efficacy of NPIs designed to prevent their spread ( Milton et al., ; Perencevich et al., ).

Many countries are appealing for greater compliance with increased and correct wearing of face masks, maintaining social distancing, adopting hand hygiene, use of personal and protective equipment (PPE), along with detection testing and contact tracing that are also referred to as 'non-pharmaceutical interventions' (NPIs) ( Rowan and Laffey, a ). The combined use of complementary NPIs are deployed to help flatten the curve of COVID-19 infections so as to particularly protect to our frontline healthcare workers (HCWs) and the most vulnerable in society ( Rowan and Laffey, a ). For example, the WHO (a) stated 'use of a mask alone is insufficient to provide an adequate level of protection, and other measures should be adopted'. The WHO (a) advises that each country apply their own risk based-approach when recommending different increasing tiers of NPIs including restrictive lockdowns, which also inflicts significant economic hardship on societies ( Rowan and Galanakis, ). The emergence of COVID-19-related 'behavioural fatigue' or 'adherence fatigue' associated with sustained societal compliance with NPIs brings added public health pressures. Michie et al. () described a Google search for 'pandemic fatigue' that resulted in approximately 200 million hits, with articles on the first page with titles such as '10 reasons why pandemic fatigue could threaten global health', and 'Europe experiencing pandemic fatigue'.

At the time of writing (8th December ), there has been, 68,225,313, cases of coronavirus disease (COVID-19) reported worldwide, including 1,556,877 deaths ( European Centre for Disease Prevention and Control, ). COVID-19 pandemic has imposed unprecedented challenges to healthcare systems ( Chowdhury et al., ), where this respiratory-virus has spread to local communities globally. COVID-19 is primarily a respiratory disease and the spectrum of infection with this virus can range from very mild, non-respiratory symptoms to severe acute respiratory illness, sepsis with organ dysfunction and death ( WHO, a ). Some people infected have reported no symptoms ( WHO, a ). There is currently a 7-day average of 204,574 new cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the United States ( Johns Hopkins University, ), which is the highest affected country for COVID-19. Several of these affected countries are experiencing peak infections rates, such as the United States, Russia and Turkey ( Table 1 ). The occurrence of third waves of COVID-19 infection that affects greater numbers of people is common for many countries globally, which puts added pressure on deploying appropriate disease-prevention counter-measures.

2. Transmission and survival of SARS-CoV ' breaking the chain of infection

2.7. Random controlled trials and risk mitigation

Wang et al. (b) was one of the earliest retrospective cohort studies (28 February to 27 March in Beijing, China) of 335 people in 124 to investigate community mask wearing, hand washing, and social distancing on COVID-19 risk reduction within families. This study confirmed that the highest risk of transmission prior to symptom onset, and provided first evidence of the effectiveness of mask use, disinfection and social distancing in preventing COVID-19. The overall secondary attack rate was 23.0% (77/335). Face masks were 79% effective and disinfection was 77% effective in preventing transmission, while calculated R0 showed that close frequent contact increased the risk of transmission 18.26 times. Household crowding was also significant; results demonstrated the involvement of pre-systematic infectiousness of COVID-19 patients (Wang et al., b).

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Chu et al. () conducted a systematic review and meta-analysis to investigate the optimum distance for avoiding person-to-person SARS-CoV-2, SARS-CoV, and MERS-CoV transmission, and to assess the use of face masks and eye protection to prevent transmission of these viruses. These authors used meta-analysis of associations of by pooling risk ratios, or adjusted odds ratios, depending on the availability from 172 observational studies across 16 countries and six continents (n = 25,697 participants), using DerSimonian and Laird random-effects models. Chu et al. () also used the Newcastle-Ottawa scale to rate risk of bias for comparative non-random studies. Risk of transmission of these viruses was lower with physical distancing of 1 m or more, compared with a distance of less than 1 m; protection was increased as distance was lengthened; face mask use could result in a large reduction in risk of infection, with stronger associations with N9 or similar respirators compared with disposable surgical masks or similar (e.g., reusable 12'16 layer cotton masks; and eye protection was associated with less infection. The primary limitation of this Chu et al. () study was that all studies were non-randomised, not always adjusted, and may suffer from recall and measurement bias (e.g., direct contact in some studies may not be measuring near distance). However, the authors found that unadjusted, adjusted, frequentist, and Bayesian meta-analyses all supported the main findings, and this approach supported the recording of large or very large effects.

Bungaard et al. () recently reported on randomised controlled trial involving Danish participants to assess whether recommending surgical masks use outside the home reduces wearers' risk of SARS-COV-2 infection in a setting where masks were uncommon and not among recommended public health measures. A total of participants were randomly assigned to the recommendation of wear masks, and were assigned to the control group; completed the study. Infection with SARS-CoV-2 occurred in 42 participants recommended to wear masks (1.8%) and 53 control participants (2.1%). Participants were adults spending more than 3 h per day outside the home without occupational mask use. Participants were encouraged to follow social distancing measures for COVID-19, but it is not possible to prove that this as achieved. The primary measurement outcome was detection of SARS-CoV-2 in the mask wearer at 1 month by antibody testing, polymerase chain reaction (PCR), or hospital diagnosis. The secondary outcome was PCR- positivity for other respiratory viruses. The authors concluded that the recommendation to wear surgical masks to supplement other public health measures did not reduce the SARS-CoV-2 rate among wearers by more than 50% in a community with modest infection rates, some degree of social distancing, and uncommon general mask use. Loeb () also described a randomised controlled trial that is ongoing in Canada in which 576 nurses will be randomised to either medical masks, or N95 respirators, when providing care to patients with COVID-19, which is due for completion on April 1, . Inclusion criteria are nurses who work >37 h per week in medical, emergency, paediatric units; while exclusion criteria are nurses with one or more comorbidities, and nurses who cannot pass an N95 respirator fit test. Ultimately, researchers have concluded that globally collaborative and well conducted studies, including randomised trials, of different personal protective strategies are needed regardless of challenges, but the current use of systematic appraisals of best available evidence could be considered to inform interim guidance (Chu et al., ).

The WHO (b) noted that 'all viruses, including SARS-CoV-2, change over time, most without a direct benefit to the virus in terms of increasing its infectiousness or transmissibility, and sometimes limiting propagation. The potential for virus mutation increases with the frequency of human and animal infections. Reducing transmission of SARS-CoV-2 by using established disease control methods as well as avoiding introductions to animal populations, are critical aspects to the global strategy to reduce the occurrence of mutations that have negative public health implications. Preliminary data suggest that the growth rate and effective reproductive number is elevated in areas of the United Kingdom with community circulation of the novel variant VOC-/01. In South Africa, genomic data highlighted that the 501Y.V2 variant rapidly displaced other lineages circulating, and preliminary studies suggest the variant is associated with a higher viral load, which may suggest potential for increased transmissibility; however, this, as well as other factors that influence transmissibility, are subject of further investigation'. The WHO has reported that epidemiologic investigations are underway to understand the increase in cases in these communities and the potential role of increased transmissibility of these variants as well as the robustness of implementation of control measures. 'While initial assessment suggests that /01 and 501Y.V2 do not cause changes in clinical presentation or severity, if they result in a higher case incidence, this would lead to an increase in COVID-19 hospitalizations and deaths' (WHO, b). More intensive public health measures may be required to control transmission of these variants. Further investigations are required to understand the impact of specific mutations on viral properties and the effectiveness of diagnostics, therapeutics, vaccines along with disinfection and NPI modalities.

Use of risk assessment (RA) to evaluate complex environmental threats is increasing in popularity. For example, Tahar et al. () reported on the development of a semi-quantitative risk assessment model for evaluating the environmental threat posed by three EU watch list pharmaceutical compounds to aquatic ecosystems. This RA model adopts the Irish EPA's Source-Pathway-Receptor concept to define relevant parameters for calculating practical low, medium or high risk scores for each agglomeration of wastewater treatment plant (WWTPs), which includes complex catchment, treatments, operational and management factors. This provides a working example where RA modelling may potentially strategically be used to unlock complex scenarios for policy decisions, such as to identify WWTPs that post a particular risk as regards releasing disproportionally high levels of pharmaceutical chemicals, and to help identify priority locations for introducing or upgrading control counter-measures (Tiedeken et al., ; Tahar et al., ; Rowan, ).

Wearing a mask can help lower the risk of respiratory virus transmission. When worn by a person with an infection, masks reduce the spread of the virus to others. Masks can also protect wearers from breathing in infectious particles from people around them. Different masks offer different levels of protection. Wearing the most protective one you can comfortably wear for extended periods of time that fits well (completely covering the nose and mouth) is the most effective option.

When choosing to wear a mask, choose the most protective type you can. Facial hair that lies along the sealing area of a respirator, such as beards, will interfere with respirators that rely on a tight facepiece seal to achieve maximum protection.

How it works

Generally, masks can help act as a filter to reduce the number of germs you breathe in or out. Their effectiveness can vary against different viruses, for example, based on the size of the virus. When worn by a person who has a virus, masks can reduce the chances they spread it to others. Masks can also protect wearers from inhaling germs; this type of protection typically comes from better fitting masks (for example, N95 or KN95 respirators).

There are many different types of masks that have varying abilities to block viruses depending on their design and how well they fit against your face. Cloth masks generally offer lower levels of protection to wearers, surgical/disposable masks usually offer more protection, international filtering facepiece respirators (like KN95 respirators) offer even more, and the most protective respirators are NIOSH Approved® filtering facepiece respirators (like N95® respirators).

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