With the enhanced virulence of the Omicron variant, some experts are urging us all to upgrade cloth and surgical masks to the much more protective N95s, but supply remains a concern. The limited supply is why this advice has so far been held back, but a new study may make this more feasible – suggesting N95s can be safely decontaminated many times in a clinical setting.

The study tested to see if these respirators deteriorate after decontamination – a process where the mask is exposed to UV light or vaporized hydrogen peroxide (VHP) to kill any SARS-CoV-2 virus particles that might have stuck around.

While early in the pandemic research indicated that an N95 could be decontaminated and reused a couple of times without being compromised, a new study from a team at Beth Israel Deaconess Medical Center in Boston has now shown that even after 25 rounds of VHP decontamination, the N95 respirator was just as good at fitting on the face and filtrating particles.

N95 respirators are a type of mask fitted very closely to the face to create a seal. To be classed as an N95 respirator, the protective device must meet the US National Institute for Occupational Safety and Health N95 classification of air filtration – which means it filters at least 95 percent of airborne particles.

"Most VHP studies were limited to evaluating decontamination efficacy, respirator filtration after 5-10 cycles, or fit on mannequins," the team writes in their new study.

"We sought to determine whether repeated VHP reprocessing would affect N95 respirator integrity as defined by qualitative and quantitative fit and filtration efficiency over 25 reprocessing cycles."

From June to August 2020, the researchers assessed seven volunteers who were using 3M 1860/1860S N95 respirators. Each volunteer was fitted for an appropriately sized mask (called fit testing), and then the team used VHP to decontaminate the respirators after use.

After the hydrogen peroxide had broken down, they returned the respirators to the volunteers, who were asked to perform a user seal check. They then did this for 25 decontamination cycles – with a user seal check after each cycle.

Every few cycles a quantitative fit test was conducted – this is where specialized equipment checks how much air is leaking through the seal. Every five cycles a filtration efficiency testing and a qualitative fit test – a test where the mask fails if the volunteer can taste or smell anything while wearing the mask – was undertaken. After 25 decontamination cycles, the team found no changes from before the first cycle to the end.

Although the masks might have lasted even longer, the researchers stopped at 25 because an FDA report has already found that by 35 cycles the straps start to degrade.

Unfortunately, most of us don't have access to a specialized sterilization chamber for doing VHP. However, all hope is not lost – there are other ways to sterilize an N95 mask at home.

Another recent study published in PLOS One found that dry heat (like the one found in an oven) can also work. At 100 degrees Celsius (212 degrees F), 30 minutes was enough to kill SARS-CoV-2 virus particles but not damage the mask. This team of researchers specifically used a walk-in oven rather than a regular one, with only four types of respirators typically used in large health care facilities, so your results may vary. They also did the method only once, so heat decontamination may not be as long lasting as the VHP decontamination, although more widely available.

In the meantime, this VHP research shows that medical staff don't need to be replacing masks every few uses to keep them up to code after decontamination.

"The findings from our study expand upon previous findings and show that VHP is a relatively safe method for reprocessing N95 respirators and could help address shortages in future epidemics," said first author of the VHP paper, Christina F. Yen, who now works at University of Texas, Southwestern.

"It is important that we now find ways to scale and translate this disinfection capability to smaller hospitals and resource-limited healthcare settings that could benefit just as much – perhaps more – from this type of personal protective equipment reprocessing in future disaster scenarios."

The new research has been published in the American Journal of Infection Control.