Viral Filtration Efficiency of Fabric Masks Compared with Surgical and N95 Masks

In response to the Coronavirus Disease 2019 (COVID-19) pandemic, current modeling supports the use of masks in community settings to reduce the transmission of SARS-CoV-2. However, concerns have been raised regarding the global shortage of medical grade masks and the limited evidence on the efficacy of fabric masks. This study used a standard mask testing method (ASTM F2101-14) and a model virus (bacteriophage MS2) to test the viral filtration efficiency (VFE) of fabric masks compared with commercially available disposable, surgical, and N95 masks. Five different types of fabric masks were purchased from the ecommerce website Etsy to represent a range of different fabric mask designs and materials currently available. One mask included a pocket for a filter; which was tested without a filter, with a dried baby wipe, and a section of a vacuum cleaner bag. A sixth fabric mask was also made according to the Victorian Department of Health and Human Services (DHHS) guidelines (Australia). Three masks of each type were tested. This study found that all the fabric masks had a VFE of at least 50% when tested against aerosols with an average size of 6.0 µm (VFE_{(6.0 µm)}). The minimum VFE of fabric masks improved (to 63%) when the larger aerosols were excluded to give and average aerosol size of 2.6 µm (VFE_{(2.6 µm)}), which better represents inhaled aerosols that can reach the lower respiratory system. The best performing fabric masks were the cotton mask with a section of vacuum cleaner bag (VFE_{(6.0 µm)} = 99.5%, VFE_{(2.6 µm)} = 98.8%) or a dried baby wipe (VFE_{(6.0 µm)} = 98.5%, VFE_{(2.6 µm)} = 97.6%) in the pocket designed for a disposable filter, the mask made using the Victorian DHHS design (VFE_{(6.0 µm)} = 98.6%, VFE_{(2.6 µm)} =99.1%) and one made from a layer of 100% hemp, a layer of poly membrane, and a layer of cheesecloth (VFE_{(6.0 µm)} = 93.6%, VFE_{(2.6 µm)} = 89.0%). The VFE of two surgical masks (VFE_{(6.0 µm)} = 99.9% and 99.6%, VFE_{(2.6 µm)} = 99.5% and 98.5%) and a N95 masks (VFE_{(6.0 µm)} = 99.9%, VFE_{(2.6 µm)} = 99.3%) were comparable to their advertised bacterial filtration efficacy. This research supports the use of fabric masks in the community to prevent the spread of SARS-CoV-2; however, future research is needed to explore the optimum design in ensuring proper fit. There is also a need for mass education campaigns to disseminate this information, along with guidelines around the proper usage and washing of fabric masks.