What level of protection do different grades of mask offer against Covid-19 transmission and infection?

What Level of Protection Do Different Grades of Mask Offer Against COVID-19 Transmission and Infection?

There are several types of mask in use worldwide, ranging from home-sewn fabric masks to clinical-grade coverings. In the following section, we present information on their effectiveness and evidence for their use. Note that no mask can be guaranteed 100% effective. Their incorrect use, or adjusting masks — and therefore touching the face repeatedly, can potentially increase the risks in some cases.

We discuss outcomes when the masks are used as per the manufacturer’s recommendations. General advice on infection control for Covid-19, including mask wearing, can be sourced from various international government agencies for infections control, for example in Switzerland, UK, the European Center for Disease Prevention, and the UAE.

Fabric masks The use of fabric face coverings has been recommended in some nations including the US, Czech Republic and India. Research into their use for SARS-Cov-2 is limited. However, existing studies suggest that masks made from cloth or household fabrics are less effective in filtering pathogens than surgical or respirator masks, but can offer some protection.

RM Medical - A Complete Guide To Face Mask Use in Clinical and Public Settings

For example, a study comparing cloth masks, (teacloth material in this study), surgical masks and FFP2 respirator masks as a form of protection from respiratory infections, showed they all conferred benefits to others from transmission, and the wearer from infection [van der Sande et al., 2008]. Cloth masks had 50% of the protection of surgical masks for the transmission of respiratory infections, whilst FFP2 respirator masks, (equivalent to N95 in the US), were 25 times as effective as surgical masks.

Another research paper, [Davies, A et al 2013], examining the transmission of influenza virus, concluded that fabric masks could stop up to 72% of virus particle spread from aerosol transmission, dependent on the fabric density and weave — dishcloth material was much more effective than cotton for example. Surgical masks offered a superior protection of 90%.

In addition, a recent evidence paper from eminent scientists in the field of viral epidemics (known as the DELVE group) submitted to the UK government, collated diverse evidence fully supporting the use of face masks, including fabric ones, in a public setting to tackle the coronavirus pandemic.

Surgical masks (including Type IIR) Surgical masks refer to loose fitting pleated coverages, looped over the ears, which are routinely used for surgical procedures. They typically comprise three layers, with a filtration barrier layer (such as melt-blown polypropylene) usually separating an inner and outer layer.

Surgical masks are intended for single use, as exhaled moisture can build up over hours making the mask wet and reducing its filtration efficiency. It should be changed if moist, and obviously between procedures and patients. Studies indicate there is also a decrease in their performance over time due to fibre changes [Bałazy A., et al 2006].

They are designed to cover the nose, mouth and chin. They protect the wearer from splashes and droplets, and others from respiratory emissions of the wearer, filtering particles > 3 microns in diameter. There are several categories of surgical mask, including Type I, Type IR, Type II and Type IIR. Note that Type I masks are not intended for use by healthcare professionals. The surgical mask classifications differ in their bacterial and particle filtration efficiency (BFE/PFE), Type I, and Type IR face masks confer 95%, whereas Type II and Type IIR provide 98%.

Furthermore, the ‘R’ label indicates that the mask has been tested for fluid or splash resistance using synthetic blood to a pressure ≥16 kPa (120 mm Hg). The latter corresponds to the average systolic arterial blood pressure.

Surgical masks are intended for single use, as exhaled moisture can build up over hours making the mask wet and minimising its filtration efficiency. It should be changed if moist, and obviously between procedures and patients. Studies indicate there is also a decrease in their performance over time due to fibre changes [Bałazy A., et al 2006].

Type II R is the standard mask used in Europe for surgical procedures and must meet the European standard EN 14683. The US equivalent is sometimes referred to as a Level 2 mask and must comply with ASTM standards*. This type of mask has a 3 or 4-ply pleated format, and is splash resistant against blood and bodily fluids. Note that surgical masks differ to respirators, (discussed below) in that the former show some leakage around the edges of this mask when the user inhales, therefore offering lower levels of protection.

Recent studies show that the use of surgical masks can provide high efficacy against virus shedding in exhaled breath. Coronaviruses were shown to be absent from droplet and aerosol samples from symptomatic individuals wearing surgical masks, but were detected in 30% and 40% of those not wearing masks [Leung et al., 2020]. Other research groups have shown up to 90% negation of virus particle spread with surgical mask use in influenza [van der Sande M. et al 2008; Davies, A et al 2013].

‘wearing of face masks in public corresponds to the most effective means to prevent inter-human transmission of Covid-19’ [Zhang, et al., 2020]

Respirator masks Respirator masks, differ to surgical masks in that they are close fitting, and are designed to create a facial seal when fitted correctly to the wearer before use. They aim to cover the nose, mouth and chin, often coming with nose clips and elasticated straps to fit around the users head to hold them in place and enable a tight seal.

Some model variations of respirators have exhalation valves, to enable easier breathing and eliminate heat build-up, however, these should not be used when sterile conditions are needed. Any air exhaled through the valve has not been filtered, thus the wearer is protected, but individuals in the vicinity of the wearer will not be protected.

A recently published meta-analysis and review investigated the use of face masks in 172 observational studies from 16 countries in avoiding the transmission of SARS-Cov-2 (Covid-19) (Chu, DK et al 2020].

One outcome of the analysis showed that N95 standard, or equivalent respirator masks were much more strongly associated with protection from viral transmission in clinical setting than surgical masks. Other conclusions showed added benefits from eye protection, and social distancing of >2M.

This concurs with prior studies showing that FFP2/N95 grade respirator masks showed lower levels of virus particle penetration [Bałazy, A et al., 2006] and significantly reduced the viral transmission of respiratory infections in public settings [van der Sande et al., 2008] when compared to surgical masks.

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Bałazy A, Toivola M, Adhikari A, Sivasubramani SK, Reponen T, Grinshpun SADo. 2006. N95 respirators provide 95% protec¬tion level against airborne viruses, and how adequate are surgical masks? Am J Infect Control. 2006 Mar; 34(2):51-7.

Chu, DK, Akl, EA, Dudaet, S 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, 2020; DOI: 10.1016/ S0140-6736(20)31142-9

Davies A, Thompson KA, Giri K, Kafatos G, Walker J, Bennett A. 2013. Testing the efficacy of homemade masks: would they protect in an influenza pandemic? Disaster Med Public Health Prep. 7(4):413-418. doi:10.1017/dmp.2013.43

Van der Sande M, Teunis P, Sabel, R. 2008. Professional and home-made face masks reduce exposure to respiratory infections among the general population. PLoS One (doi: 10.1371/journal.pone.0002618).