A randomized trial indicating that surgical masks are not inferior to N95 masks in protecting healthcare workers against COVID-19 has drawn international criticism.
The study’s lead author is John Conly, MD, an infectious disease specialist and professor at the University of Calgary Cumming School of Medicine, Calgary, Alberta, Canada and Alberta Health Services. The findings are not consistent with those of many other studies on this topic.
Commenting on the Conly study on Twitter, Eric Topol, MD, editor-in-chief of medscapeHe wrote: “Unfortunately underpotent, but ruled out doubling the risk from the use of medical masks.”
The study, which was partially funded by the World Health Organization (WHO), was published online November 29 at Annals of Internal Medicine.
This is not the first time that Conly, who also advises the WHO, has been the subject of controversy. She previously denied that COVID-19 is airborne, a position contradicted by solid evidence. Last year Conly hit the headlines with his controversial claim that N95 respirators can cause harm, including oxygen depletion and carbon dioxide retention.
A detailed examination by the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota, Minneapolis, pointed out numerous scientific flaws in the study, including the inconsistent use of both types of masks. The study also looked at health workers in four very different countries (Canada, Israel, Egypt, and Pakistan) during different periods of the pandemic, which may have affected the results. In addition, the study did not take vaccination status into account and lacked a control group. CIDRAP receives funding from 3M, which makes N95 respirators.
In a comment Published along with the study, Roger Chou, MD, a professor of medicine at Oregon Health & Science University in Portland, said the results were “not definitive,” with “a generous non-inferiority threshold” which it actually is.” consistent with up to a relative 70% increased risk…which may be unacceptable to many healthcare workers.”
The study’s lead author, Mark Loeb, MD, a professor of infectious diseases at McMaster University in Hamilton, Ontario, Canada, defended the findings. “The confidence intervals around this, that is, what the possible results might be if the test were repeated many times, range from -2.5% to 4.9%,” he said. medscape. “This means that the risk of a COVID-19 infection in those who wear the medical masks could have ranged from a 2.5% risk reduction to a 4.9% increased risk. Readers and policy makers can decide for themselves on this.”
“There is no point in continuing to conduct poorly designed and underpowered studies that are designed to confirm existing biases,” said Raina MacIntyre, PhD, professor of global biosafety and director of the Biosafety Program at the Kirby Institute, in Sydney, Australia. medscape. “The new study in Annals of Internal Medicine is completely consistent with our finding that to prevent infection, you need an N95 and it should be worn throughout the shift. A surgical mask and intermittent use of N95 are equally ineffective. This shouldn’t surprise anyone, given that a surgical mask is not designed for respiratory protection, but rather to prevent splashing or splashing of liquid onto the face. Only a respirator is designed for respiratory protection through the around-the-face seal and facepiece filter to prevent inhalation of virus-laden aerosols, but you must wear it continuously in a high-risk environment such as a hospital.
“It doesn’t make sense to do a randomized trial on something that can be measured directly,” Kimberly Prather, PhD, atmospheric chemist, professor and director of the NSF Center for Aerosol Impacts on the Chemistry of the Environment at the University of California, San Diego, said medscape. “In fact, many studies have shown that aerosols escape from surgical masks. Surgical masks are designed to block large aerosol droplets. Aerosols (0.5 to 3 µm), which have been shown to contain the infectious virus SARS-CoV-2, they travel with the airflow, and escape.”
“This study…will be used to justify policies to provide healthcare workers, and perhaps also patients and visitors, with inadequate protection,” Trish Greenhalgh, MD, professor of primary care health sciences at Oxford University, Oxford, United Kingdom, said medscape.
“These authors have been rejecting treatment of COVID as airborne for 3 years,” said David Fisman, MD, an epidemiologist and infectious disease specialist at the University of Toronto Dalla Lana School of Public Health, Toronto, Ontario, Canada. medscape. “So you will see these people brandishing this very flawed assay to justify continuing the infection control practices that have been so disastrous during the pandemic.”
The study was funded by the World Health Organization, the Canadian Institutes for Health Research and the Juravinski Research Institute. Conly reported receiving grants from the Canadian Institutes for Health Research, Pfizer and the WHO. Chou co-authored with one of the authors of Loeb’s study on a similar topic. He also revealed to be a methodologist of the WHO guidelines on infection prevention and control measures for COVID-19. Loeb disclosed payment for expert testimony on personal protective equipment from the Manitoba government and the Peel District School Board. MacIntyre has conducted extensive research on masks and respirators in healthcare workers, including four randomized clinical trials. She is the author of a book, Dark Winter (NewSouth, 2022), covering the history and politics of the controversies surrounding N95s and masks. Prather did not report disclosures. Greenhalgh is a member of Independent WISE and unpaid advisor to the Balvi philanthropic fund. Fisman has served as a paid legal expert for the Ontario Nurses Association in its challenge to Directive 5, which restricted access to N95 masks in healthcare. She also served as a paid legal expert for the Ontario Federation of Elementary Teachers in their efforts to make schools safer in Ontario.
kate johnson is a Montreal-based freelance medical journalist who has been writing for more than 30 years on all areas of medicine.