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Expired as well as fresh N95 respirators cleaned with hydrogen peroxide solution retained over 95% of fitted filtration efficiency, a small laboratory study found.

N95 respirators in the wrong size had around 90%-95% fitted filtration efficiency, while two imported respirators authorized by the CDC, but not approved by the National Institute for Occupational Safety and Health (NIOSH), were much less effective, reported Emily Sickbert-Bennett, PhD, of UNC Healthcare in Chapel Hill, and colleagues writing in

Shortage of personal protective equipment during COVID-19 forced the CDC to develop "contingency and crisis strategies to provide alternatives for respirators," the authors noted. However, they added that comparative fitted filtration efficiencies, including filtering efficiency of material and fit to the face, for these respirator alternatives have yet to be quantified, and "health care facilities are faced with prioritization of their available options without clear data to guide decision-making."

An by Caitlin Dugdale, MD, and Rochelle Walensky, MD, both of Massachusetts General Hospital in Boston, characterized these findings as "reassuring evidence" of the performance of non-standard approaches to "preserving the N95 mask supply."

While they acknowledged recent efforts to recommend additional precautions for healthcare professionals against aerosol transmission, Dugdale and Walensky noted "the viability and infectiousness of SARS-CoV-2 viral particles in aerosol form remains unknown."

"Importantly, no documented SARS-CoV-2 outbreaks have been linked to settings in which surgical masks were assiduously used in lieu of N95 masks, which suggests that even if airborne transmission is a considerable contributor to SARS-CoV-2 transmission, surgical masks are likely sufficient to prevent it," the editorialists wrote.

Dugdale and Walensky also addressed the issue of cost, which is "a major challenge in procurement of adequate mask supply," and called upon healthcare organizations to continue to find "innovative ways to overcome PPE shortages."

While NIOSH-approved N95 respirators should be reserved for frontline clinicians and "essential healthcare workers who engage in the highest risk procedures," Dugdale and Walensky argued that "surgical masks and other N95 alternatives likely provide adequate protection against transmission for routine care."

Study details

Sickbert-Bennett and colleagues conducted fitted filtration efficiency tests this spring on 29 different respirator mask products.

The face mask alternatives were fitted on one adult man and one adult woman, and fitted filtration efficiency was measured over a series of repeated movements of "torso, head, and facial muscles" that simulated "typical occupational activities experienced by a mask wearer."

Among the "commonly used" products tested, the MAXAIR Controlled Air Purifying Respirator, the Halyard Health N95, and the 3M 1870+ Aura all blocked more than 99% of particles. Two other 3M products (8210 and 1860) showed efficiencies of between 97% and 99%.

As well, 3M 1860 and 8210 respirators that expired in 2009 and 2011, along with newer 3M products sanitized with ethylene oxide or vaporized hydrogen peroxide, both retained fitted filtration efficiency rates over 95%. These rates were comparable to those found with new 3M N95 respirators.

Among less commonly used products, the researchers found seven that exceeded 95% efficiency: two Dasheng models, two from 3M, and three from lesser known manufacturers. All are NIOSH approved.

But none of the new-in-the-box respirators not approved by NIOSH -- including the Dasheng DTC-3X-1 and DTC-3X-2 that the CDC authorized -- achieved 95% fitted filtration efficiency. The DTC-3X1 with ear loops was about 80%, and the DTC-3X2 with ear loops was about 77%. For two KN95 masks tested, one had efficiency of 85% and the other 53%.

Dugdale and Walensky noted that millions of KN95 masks were "purchased or donated to U.S. hospitals" during the pandemic.

Sickbert-Bennett and colleagues also found that tie-on surgical masks clocked in at about 72% fitted filtration efficiency; surgical masks with ear loops fared the worst, at 38%.

When examined by sex, the small 3M 1860 N95 respirator on the man and the regular version on the woman did not achieve a fitted filtration efficiency of more than 95%, though it was over 90%, and all other single-sized N95 masks did achieve that benchmark.

Limitations to the data included that the masks were only tested by one man and one woman rather than more individuals with "a full range of facial configurations."

"This evaluation provides quantitative results on which health care administrators, supply chain leaders, and hospital epidemiologists can make evidence-based decisions to protect clinicians and other health care workers during a pandemic or long-term mask shortage," Sickbert-Bennett and colleagues concluded.

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