Tests of commonly available fabric masks by scientists at Flinders University has concluded that they significantly reduce the number of aerosolised viruses a wearer could be exposed to.
The study, published in Pathogens, found even the poorest performing mask filtered at least 50% of viruses.
The viral filtration (VFE) was calculated for two sizes of aerosols, 6 microns (VFE 6 μm), which is the size of aerosols produced by coughing, and 2.6 microns, which are small enough to be inhaled into the lower respiratory system.
The best performing fabric masks filtered 97% to 99% of the virus at both VFE measures.
One mask, made according to the Victorian Department of Health and Human Services guidelines, with two layers of reusable shopping bag fabric and one layer of cotton, filtered performing at 98.6% of the 6 micron particles and 99.1% of the 2.6 ones.
Another mask made from two layers of cotton had a VFE 6.0 μm of 55% and a VFE 2.6 μm of 93%. However, the effectiveness of that mask increased to become one of the best performers by simply inserting a section of vacuum cleaner bag or a dried baby wipe.
This study also found the VFE of N95 and surgical masks supported their high advertised bacterial filtration efficiency.
The Flinders environmental health experts said that while a 50% reduction might not seem particularly effective, US modelling studies have shown that if 80% of the population was wearing a 50% effective mask in areas of high transmission like New York, the number of COVID-19 deaths could fall between 17% and 45%.
This predicted reduction in deaths is significantly increased by wearing masks in areas with lower transmission rates, the researchers say.
Flinders University scientist Dr Harriet Whiley the study offered useful guidance for people required to wear face masks in public during the COVID-19 pandemic,” says
“The information will also inform best practice for fabric face mask design to protect against respiratory diseases and reduce community-based transmission of SARS-CoV-2 – the virus that causes Covid-19.”
She explains their findings below: