When the researchers compared wearing masks to wearing no protection during 20-minute and 30-second exposures to the virus, they found that infection risks were reduced by 24-94% or by 44-99% depending on the mask and exposure duration. Risk reduction decreased as exposure duration increased, they found.
"N99 masks, which are even more efficient at filtering airborne particles than N95 masks, are obviously one of the best options for blocking the virus, as they can reduce average risk by 94-99% for 20-minute and 30-second exposures, but they can be hard to come by, and there are ethical considerations such as leaving those available for medical professionals," Wilson said.
The next best options, according to the research, are N95 and surgical masks and, perhaps surprisingly, vacuum cleaner filters, which can be inserted into filter pockets in cloth masks. The vacuum filters reduced infection risk by 83% for a 30-second exposure and 58% for a 20-minute exposure. Of the other nontraditional materials evaluated by the researchers, tea towels, cotton-blend fabrics and antimicrobial pillowcases were the next best for protection.
Scarves, which reduced infection risk by 44% after 30 seconds and 24% after 20 minutes, and similarly effective cotton t-shirts are only slightly better than wearing no mask at all, they found.
"We knew that masks work, but we wanted to know how well and compare different materials' effects on health outcomes," said Wilson, who specializes in quantitative microbial risk assessment. Wilson and her team collected data from various studies of mask efficacy and created a computer model to simulate infection risk, taking various factors into consideration.
The model developed by Wilson and her colleagues included parameters such as inhalation rate - the volume of air inhaled over time - and virus concentration in the air.
"We took a lot of research data, put it into a mathematical model and related those data points to each other," Wilson said. "For example, if we know people's inhalation rates vary by this much and know this much virus is in the air and these materials offer this much efficiency in terms of filtration, what does that mean for infection risk? We provide a range, in part, because everyone is different, such as in how much air we breathe over time."
MEDICA-tradefair.com; Source: University of Arizona
