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Reused and out-of-date N95 masks still effective at preventing COVID-19

NIOSH-rated masks can also be subjected to sterilization with hydrogen peroxide or ethylene oxide without compromising efficiency.

Jeff Lagasse, Associate Editor

This spring, due to limited national supplies of N95 face masks, hospitals across the country asked private companies and the public to donate personal protective equipment, including many different types of masks, to ensure healthcare workers were protected while caring for patients.

With so many options, infection-prevention experts at the UNC Medical Center set out to gather evidence on the fitted filtration efficiency of dozens of different types of masks and mask modifications, including masks sterilized for reuse, expired masks, novel masks obtained from domestic and overseas sources, and homemade masks.

The data, published in JAMA Internal Medicine, show that reused, sterilized N95 masks and very out-of-date N95 masks retain their effectiveness at protecting healthcare workers from COVID-19 infection.

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To assess the masks' fitted filtration effectiveness, Dr. Emily Sickbert-Bennett, director of infection prevention at UNC Medical Center, turned to someone she knew she could trust: her father, Dr. William Bennett, a professor of medicine who leads the Mucociliary Clearance and Aerosol Research Laboratory at the UNC Center for Environmental Medicine, Asthma and Lung Biology. He volunteered to test the masks in his lab.

Thanks to a cooperative agreement with the EPA Human Studies Facility on the UNC-Chapel Hill campus, where Bennett's labs reside, Bennett, assistant professor Dr. Phillip Clapp and research associate Dr. Kirby Zeman teamed with EPA research scientist Dr. James Samet to measure the fraction of submicron particles that penetrate into the breathing space of subjects wearing a mask while performing a series of tasks that simulate conditions such as speech and movement during a work shift. Such tests provided infection-prevention leaders with quantitative data they used to rank the best respiratory-protection options for healthcare personnel during the COVID-19 outbreak.

They found that certain N95 masks -- as rated by the National Institute of Occupational Safety and Health Administration -- provide greater than 95% effectiveness at keeping the wearer from inhaling very small airborne particles that may carry SARS-CoV-2, the virus that can cause COVID-19.

These masks also retain such effectiveness many years beyond their expiration dates. And these NIOSH-rated masks can be subjected to sterilization with hydrogen peroxide or ethylene oxide without compromising their efficiency. 

On top of that, their fitted filtration procedures showed that surgical masks with ties were about 70% effective at filtering their inhaled particles, while surgical masks with ear loops were about 40% effective.

One of the keys to protection is how snug a mask fits. An N95 mask that forms a tight seal offers the optimal infection prevention, but evidence from previous studies suggests that even the surgical masks with less than 95% efficiency are effective in preventing acquisition of epidemic coronaviruses.


Nearly 90% of healthcare providers are contributing to stockpiles of critical medical supplies and drugs intended to last as long as 90 days, according to a recent survey conducted by healthcare improvement company Premier. 

But as new COVID-19 hotspots emerge, the survey shows local efforts to build stockpiles must be supported with a national strategy to avoid redirecting supplies away from frontline caregivers and exacerbating ongoing product shortages. Either the health system or the state is directing the majority of stockpiling efforts, although product backorders are inhibiting requests to replenish stockpiles and are interfering with timely care.

The products that providers cited as heavily backordered include N95 masks and bouffant caps (both cited by 53% of respondents); isolation gowns and shoe covers (49%); testing swabs and test kits (40%); surgical gowns (35%); exam gloves (32%); surgical masks (30%); and syringes (7%).

Research now shows that different types of masks are more effective at preventing COVID-19 transmission than others. Some easily accessible cloth masks are about as effective as standard surgical masks, while alternatives such as neck gaiters, which are made of thinner material, may in fact be worse than not wearing a mask at all.

Twitter: @JELagasse
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