• Mark Loeb, Amy Bartholomew, Madiha Hashmi, Wadea Tarhuni, Mohamed Hassany, Ilan Youngster, Ranjani Somayaji, Oscar Larios, Joseph Kim, Bayan Missaghi, Joseph V Vayalumkal, Dominik Mertz, Zain Chagla, Maureen Cividino, Karim Ali, Sarah Mansour, Lana A Castellucci, Charles Frenette, Leighanne Parkes, Mark Downing, Matthew Muller, Verne Glavin, Jennifer Newton, Ravi Hookoom, Jerome A Leis, James Kinross, Stephanie Smith, Sayem Borhan, Pardeep Singh, Eleanor Pullenayegum, and John Conly.
• Department of Pathology and Molecular Medicine and Department of Health Research Methods, Evidence, and Impact, McMaster University, Hamilton, Ontario, Canada (M.L.).
• Ann. Intern. Med. 2022 Dec 1; 175 (12): 162916381629-1638.

BackgroundIt is uncertain if medical masks offer similar protection against COVID-19 compared with N95 respirators.ObjectiveTo determine whether medical masks are noninferior to N95 respirators to prevent COVID-19 in health care workers providing routine care.DesignMulticenter, randomized, noninferiority trial. (ClinicalTrials.gov: NCT04296643).Setting29 health care facilities in Canada, Israel, Pakistan, and Egypt from 4 May 2020 to 29 March 2022.Participants1009 health care workers who provided direct care to patients with suspected or confirmed COVID-19.InterventionUse of medical masks versus fit-tested N95 respirators for 10 weeks, plus universal masking, which was the policy implemented at each site.MeasurementsThe primary outcome was confirmed COVID-19 on reverse transcriptase polymerase chain reaction (RT-PCR) test.ResultsIn the intention-to-treat analysis, RT-PCR-confirmed COVID-19 occurred in 52 of 497 (10.46%) participants in the medical mask group versus 47 of 507 (9.27%) in the N95 respirator group (hazard ratio [HR], 1.14 [95% CI, 0.77 to 1.69]). An unplanned subgroup analysis by country found that in the medical mask group versus the N95 respirator group RT-PCR-confirmed COVID-19 occurred in 8 of 131 (6.11%) versus 3 of 135 (2.22%) in Canada (HR, 2.83 [CI, 0.75 to 10.72]), 6 of 17 (35.29%) versus 4 of 17 (23.53%) in Israel (HR, 1.54 [CI, 0.43 to 5.49]), 3 of 92 (3.26%) versus 2 of 94 (2.13%) in Pakistan (HR, 1.50 [CI, 0.25 to 8.98]), and 35 of 257 (13.62%) versus 38 of 261 (14.56%) in Egypt (HR, 0.95 [CI, 0.60 to 1.50]). There were 47 (10.8%) adverse events related to the intervention reported in the medical mask group and 59 (13.6%) in the N95 respirator group.LimitationPotential acquisition of SARS-CoV-2 through household and community exposure, heterogeneity between countries, uncertainty in the estimates of effect, differences in self-reported adherence, differences in baseline antibodies, and between-country differences in circulating variants and vaccination.ConclusionAmong health care workers who provided routine care to patients with COVID-19, the overall estimates rule out a doubling in hazard of RT-PCR-confirmed COVID-19 for medical masks when compared with HRs of RT-PCR-confirmed COVID-19 for N95 respirators. The subgroup results varied by country, and the overall estimates may not be applicable to individual countries because of treatment effect heterogeneity.Primary Funding SourceCanadian Institutes of Health Research, World Health Organization, and Juravinski Research Institute.

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