A randomized, controlled trial (RCT) among health care workers comparing fit-tested N95 masks (n=507), to medical masks (n=497) just published 11/29/22 in the pre-eminent internal medicine journal Annals of Internal Medicine, found SARS-CoV-2 infection rates did not differ between the groups. Confirmed (by RT-PCR) SARS-CoV-2 infections occurred in 52/497 (10.46%) of those assigned to medical masks, vs. 47/507 (9.27%) assigned to fit-tested N95 masks (hazard ratio 1.14 [95% CI, 0.77-1.69).
The study’s authors, Dr. Mark Loeb of McMaster University, and colleagues, refused to contextualize, honestly, their negative findings within the considerably larger universe of null RCT data comparing both medical masks to no masking (14 studies, 10 here; also here, here, here, here*, *see below), or N95 masks to medical masks (2 prior studies; here, here), for the prevention of respiratory viral infections, notably influenza, but also coronavirus infections, both non-SARS human coronaviruses, and SARS-CoV-2. For example, Loeb and colleagues cite Abaluck et al maintaining their study demonstrated a “reduction in SARS-CoV-2 with medical masks,” among Bengladeshi villagers. Notwithstanding this claim, appropriate re-evaluations of the invalid Abaluck et al analyses by renowned biostatisticians (here, here, here), using the original raw dataset, revealed no effect of medical masks vs. no masks on community SARS-CoV-2 infection rates.
Moreover, Loeb et al ignore the negative DANMASK community RCT of medical masks vs. no masks, for the prevention of SARS-CoV-2 (also published in the Annals of Internal Medicine!), as well as 12 negative community RCTs of medical masks vs. no masks for the prevention of (primarily) influenza (10 here; also here, here). It is imperative to understand that both influenza and coronavirus are disseminated by micro-aerosols and their particle diameters are in the 80-140 nanometer diameter range (here; here; here; here). These physical properties render the viruses well below the efficient filtering thresholds of N95 (here), let alone medical, or cloth masks.
First author Loeb even failed to cite his own negative 2009 RCT conducted among emergency room nurses (published in JAMA) comparing fit-tested N95 masks (n=210) to medical masks (n=212) for influenza prevention. A secondary analysis from Loeb’s 2009 RCT found, additionally, no beneficial impact of N95 vs. medical masks on non-SARS human coronavirus infection rates. Most egregiously, Loeb et al also ignored Radonovich et al’s 2019 “cluster-randomized” RCT published in JAMA, comparing the impact of fit-tested N95 masks to medical masks on influenza infection rates, among 2862 health care workers. Nearly 3-fold as large as the 11/29/22 study reported by Loeb et al, Radonovich et al concluded, verbatim:
“[T]here was no significant difference between the effectiveness of N95 respirators and medical masks in preventing laboratory-confirmed influenza among participants routinely exposed to respiratory illnesses in the workplace. In addition, there were no significant differences between N95 respirators and medical masks in the rates of acute respiratory illness, laboratory-detected respiratory infections, laboratory-confirmed respiratory illness, and influenza like illness among participants.”
 “The major implication of this study is that protection with a surgical mask against influenza appears to be similar to the N95 respirator, meeting criteria for noninferiority. Our findings apply to routine care in the health care setting… In routine health care settings, particularly where the availability of N95 respirators is limited, surgical masks appear to be non-inferior to N95 respirators for protecting health care workers against influenza.”
 “Among health care workers who took care of patients with suspected or confirmed COVID-19, although the upper limit of the CIs of the pooled estimate for medical masks when compared with N95 respirators for preventing RT-PCR–confirmed COVID-19 was within the noninferiority margin of 2, this margin was wide, and firm conclusions about noninferiority may not be applicable given the between-country heterogeneity… In conclusion, among 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.”
Links to full pdf versions of the three RCTs comparing N95 and medical masks, and key tables and figures for these studies, are provided below.
Full pdf link to 2009 RCT comparing N95s and medical masks for influenza prevention: RCT N95 no better than med masks 2009 jama
Full pdf link to 2019 RCT comparing N95s and medical masks for influenza prevention: N95 Respirators vs Medical Masks for Preventing Influenza
Full pdf link to 2022 RCT comparing N95s and medical masks for SARS-CoV-2 prevention: Annals N95 vs. Surg masks C19 rct