US healthcare workers have faced a shortage of N95 masks since March, when the coronavirus began spreading rapidly.

A study of 29 types of masks used in healthcare settings showed expired and used N95s blocked coronavirus particles just as well as newer ones.

Surgical masks blocked fewer particles than N95s but were still effective. 

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The US has spent months dealing with shortages of N95 masks — the type that works best to protect people from the coronavirus. Healthcare workers have had to make do with expired and used N95s despite questions about their effectiveness. 

Now those workers can perhaps breathe a little easier: A study published Tuesday in the journal JAMA Internal Medicine showed that used and expired N95 masks may be just as effective as new ones.

In the study, researchers at the University of North Carolina at Chapel Hill tested the filtration ability of 29 types of face masks commonly used in hospital settings, including new, expired, and used N95 masks, as well as surgical masks with ties and ear loops.

The results showed that N95 masks — even expired ones and masks that had been used once then sanitized and reused — worked much better than surgical masks, blocking nearly all airborne particles. Surgical masks with ties offered better protection than those with ear loops, likely because they fit more tightly. 

Testing the masks: N95s performed better than surgical masks across the board

The researchers tested all 29 types of mask on a male volunteer, while a female volunteer tested six of the most widely used masks. The study didn’t include cotton masks, bandanas, or other nonmedical masks, since its focus was on healthcare settings. 

To evaluate each mask, the researchers filled a chamber with aerosolized salt particles about the size of small coronavirus particles, then sent the volunteer in wearing that mask.

Over the next three minutes, the volunteer would repeat a series of movements designed to mimic a healthcare worker’s daily tasks: bending down and up, reading, twisting his head from side to side, and moving his head up and down. 

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At the start of 2020, the Strategic National Stockpile had barely 1% of the N95 masks that healthcare workers were expected to need.

Of all the mask types commonly used in hospital settings, surgical masks with ear loops performed worst, protecting the male volunteer from only about 40% of particles. They protected the female volunteer from just under 27%.

Surgical masks that tie at the back of the head did better, blocking nearly 72% of particles.

As expected, all N95 masks (new, used once, and expired) did better than surgical ones. In every activity, they exceeded the number in their name, blocking more than 95% of particles. In fact, none of the N95s blocked less than 96.8% of particles — not even expired masks or those that had been sanitized once with hydrogen peroxide and ethylene oxide. 

What the findings mean for healthcare workers

The researchers cautioned that their findings may not be perfect, since they tested most of the masks on only one person, and masks fit people differently depending on their head shapes. That could particularly influence the protection levels from surgical masks, since those aren’t fitted like N95s.

But varying head shapes likely wouldn’t change the researchers’ overall conclusion: Both expired and lightly used N95 masks, provided they’re properly fitted and sterilized, are still worth using in healthcare settings. 

In a commentary accompanying the study, Caitlin Dugdale and Rochelle Walensky, two infectious-disease specialists at Harvard Medical School, offered their take on the findings. 

“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,” they wrote.

The key, however, is that patients must wear the masks too.

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