Amid a worldwide shortage of N95 respirators that help protect healthcare workers on the frontlines of the COVID-19 pandemic, a new study conducted by federal scientists found that the masks can be effectively decontaminated from SARS-CoV-2 exposure and reused up to three times. While the research, published on April 15, has not been peer-reviewed, it offers multiple methods for extending the life of N95 respirators, which are designed for single use.          

Coauthor Vincent Munster of the National Institute of Allergy and Infectious Diseases tells The New York Times that the research relied upon more than a decade of studies on decontamination. “We showed that it actually works as well for SARS-CoV-2 as for influenza,” and is also effective against bacteria, he says.

The investigators tested different decontamination methods on small sections of filter fabric from N95 respirators that had been exposed to the SARS-CoV-2 virus, including vaporized hydrogen peroxide (VHP), 70 °C dry heat, ultraviolet light, and 70% ethanol spray, according to a press release. While all four methods were found to eliminate the virus, the authors concluded that the VHP method was most effective because it required only a 10-minute treatment, while UV and dry heat require at least 60-minute treatments.

Volunteer employees wore clean respirators that had been decontaminated with all four methods in order to test whether the masks maintained a proper fit and seal over the face, which is crucial for reducing exposure to airborne pathogens. Ethanol damaged the mask after two decontamination sessions, and for that reason is not recommended by the authors, according to the statement.

Even if the decontamination was successful but the mask fit was compromised, Munster tells the Times, “then obviously your mask is not really good for reuse anymore.”

UV and dry heat–treated masks held up for two cycles of decontamination but began to fail after three, suggesting that they could potentially be reused twice. VHP–treated masks were unaffected, which means they may possibly be used three times. 

“Vaporized hydrogen peroxide would be the method of choice if that’s available,” Munster tells the Times. Nursing homes may not have access to VPH, he says, but the dry heat procedure could basically be carried out in an oven. 

Lynn Goldman of George Washington University’s Milken Institute School of Public Health says in remarks to the Times that the new study is an “excellent contribution” and that it’s “helpful to see that either VHP or UV can effectively sterilize N95 masks and make them available for reuse up to three times.”

Another preprint published by researchers in Canada on April 8 found that masks of varying brands were still effective after 10 rounds of VHP decontamination, reports the Times.

The US Food and Drug Administration had previously issued emergency use authorizations for a number of mask decontamination methods, including one VHP system that could potentially decontaminate 4 million masks per day, reports Healio, and the US Centers for Disease Control and Prevention published guidelines on both extended use and limited reuse of N95 respirators.

On April 13, the Pentagon announced a $415 million contract for 60 units of the Battelle Decontamination System, each of which can decontaminate up to 80,000 respirators per day.