Experts say frontline health workers are still at high risk of COVID-19 infections, but new research published in the Journal of Infectious Diseases finds using a fit-tested N95 mask indoors along with a HEPA air filter system significantly reduces that risk.
According to the study, virus-laden aerosols remain in the air for prolonged periods and travel large distances while remaining infectious.
Study co-author, Shane Landry, PhD, Research Fellow, Sleep & Circadian Medicine Laboratory, Department of Physiology, Biomedical Discovery Institute (BDI), at Monash University, explained that they conducted this study to better understand how effective commonly used personal protective equipment (PPE) is at protecting healthcare workers from COVID-19 airborne transmission, and to assess how deployment of portable air purifiers can augment these protections.
“Frontline healthcare workers are at risk of being infected with SARS-CoV-2. The WHO estimates that about 115,500 healthcare workers died of COVID-19 between January 2020 to May 2021,” Landry told Healthline.
Researchers looked at three types of masks
Landry and team noted previous research finding that even healthcare workers (HCWs) caring for patients not undergoing aerosol-generating procedures were infected with COVID-19 despite wearing surgical masks and PPE.
Using a non-hazardous virus, they assessed the degree of personal contamination with virus aerosol when wearing different types of masks:
- Poor-fitting N95 that failed fit testing
- Fit-tested N95 that passed fit testing combined with face shield, gown, and disposable gloves
They also analyzed whether a portable HEPA filter enhanced the benefit of PPE to protect the wears against air-carried disease transmission.
The findings found only the fit-tested N95 masks had lower viral counts compared to the control group. They also found wearing a fitted N95 mask combined with HEPA filtration and other PPE gear helped bring viral exposure to nearly zero.
Landry said he wasn’t surprised by the findings.
“Surgical masks are not designed to seal, so we were not surprised that we saw virus infiltration,” he said.
He pointed out that the poor fitting N95 had failed a fit test, so they expected it to fail the challenge.
“The fact that our well fitted (passed fit-test) N95 provided the strongest protection is a good demonstration that the seal (how well it fits) is often the most important factor in mask protection,” said Landry. “Probably more important than the filtration properties of the mask medium.”
He emphasized that these findings are a “strong endorsement” for a layered approach to safety measures against COVID-19 infection.
What are high-risk settings for COVID infection?
Peter Pitts, former associate commissioner at the FDA and president of the Center for Medicine in the Public Interest, said that any setting where there are many people who are potentially from high infection/low vaccination areas could be considered high risk.
“This means settings that bring people from different geographies together, such as mass transportation, sports, venues, and … hospitals,” he said.
Pitts added that if you’re vaccinated and not at high risk for “serious” COVID-19, you have to be aware of your surroundings and determine your own risk/benefit calculations.
Pitts also said healthcare facilities are among the safest places to be relative to infection risk.
“They have excellent ventilation and social distancing protocols,” he said. “They are also acutely aware of the need to protect staff and high-risk patients from COVID-19 infection.”
Dr. Robert G. Lahita, director of the Institute for Autoimmune and Rheumatic Disease at Saint Joseph Health and author of “Immunity Strong,” says closed spaces where airflow is poor leads to a higher risk of COVID-19 infection.
“For example, a wedding,” he cautioned. “One of my nurses went to a wedding, and 70 percent of the people there became infected.”
Lahita advised that air passengers are a particular group that should be wearing N95 masks, noting that planes also use HEPA filters which further reduces risk.
Charles Bailey, MD, medical director for infection prevention at Providence Mission Hospital and Providence at St. Joseph Hospital, said that aerosol COVID transmission mostly occurs under “specific scenarios” within a healthcare setting, but the most common form of transmission by far is via droplets.
“As far as the general public is concerned, with the possible exception of those who are severely immunosuppressed,” said Bailey. “A well-fitting medical-grade mask or at most a simple unadulterated N95 is sufficient.”
Study doesn’t represent ‘normal conditions’
According to Monica Gandhi, MD, a professor of Medicine at the University of California San Francisco, this study does not represent normal conditions under which people most are exposed to viral particles.
“The evidence seems increasingly clear that cloth and surgical masks are not effective in preventing viral transmission,” she said.
But that doesn’t mean that N95 masks without fit-testing don’t provide some protection.
She confirmed that “fit and filtered masks” like N95 or KN95 provide one-way protection.
“At this point in the pandemic, public health officials can recommend one-way masking for self-protection,” Gandhi said. “But should emphasize that well-fitting and filtered masks work best.”
New research finds PPE, including well-fitting N95 masks and HEPA air filtration, works best to prevent indoor aerosol transmission of COVID-19 in high risk settings.
Experts say that mask fit is the most important factor in how well you’re protected.
They also say that one-way masking should be recommended for self-protection at this point in the pandemic, and well-fitting, filtered masks work best.