N95 or KN95 masks offer best protection, real-world study shows
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In a real-world study of face masks conducted before the omicron surge, people who reported wearing N95 or KN95 respirators in public indoor spaces were 83% less likely to test positive for SARS-CoV-2 than people who never wore a mask.
The study demonstrated that consistent use of any mask or respirator indoors was associated with lower odds of a positive test result, although respirators offered the best protection overall, followed by surgical masks, researchers reported in MMWR.
The CDC last month removed concerns about supply shortages of N95 and KN95s from its consumer COVID-19 mask guidance and said for the first time that people can wear the masks.
Healio surveyed experts soon after the shift in guidance and found that they frequently preferred wearing N95 or KN95 masks during patient encounters or in public spaces, including pubic transportation, during the omicron surge.
In the new study, Kristin L. Andrejko, BS, an infectious disease epidemiologist at the California Department of Public Health, and colleagues enrolled randomly selected California residents who had received a test result for SARS-CoV-2 between Feb. 18 and Dec. 1, 2021.
“Face masks or respirators (N95/KN95s) effectively filter virus-sized particles in laboratory settings,” they wrote. “The real-world effectiveness of face coverings to prevent acquisition of SARS-CoV-2 infection has not been widely studied.”
The test-negative design case-control study included 652 participants who had tested positive for SARS-CoV-2 and 1,176 matched controls who tested negative. All participants self-reported being in indoor public settings during the 2 weeks leading up to their tests and reported no known contact with a confirmed or suspected SARS-CoV-2 case during this time.
Overall, the study demonstrated that always wearing a face mask or respirator in indoor public settings was associated with lower adjusted odds of a positive test result compared with never wearing a face mask or respirator in these settings (adjusted OR = 0.44; 95% CI, 0.24-0.82).
Based on the 534 study participants who specified their preferred face covering, the researchers calculated that N95/KN95 respirators (aOR = 0.17; 95% CI, 0.05-0.64) and surgical masks (aOR = 0.34; 95% CI, 0.13-0.9) were associated with the lowest odds of infection compared with not wearing any face mask or respirator.
One of the limitations, the researchers said, was that the study was conducted “before the expansion” of the more transmissible omicron variant.
“The findings of this report reinforce that in addition to being up to date with recommended COVID-19 vaccinations, consistently wearing face masks or respirators while in indoor public settings protects against the acquisition of SARS-CoV-2 infection,” the authors concluded. “This highlights the importance of improving access to high-quality masks to ensure access is not a barrier to use.”
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