Richard Mark Kirkner
June 01, 2020
A study that claims to be the first review of all the available evidence of the effectiveness of physical distancing, face masks, and eye protection to prevent spread of COVID-19 and other respiratory diseases has quantified the effectiveness of these protective measures. The study found that greater physical distancing from an exposed person significantly reduces risk of transmission and that N95 masks, particularly for health care workers, are more effective than other face coverings.
The meta-analysis, published online in The Lancet (2020 Jun 2; doi.org/10.1016/ S0140-6736(20)31142-9) also marks the first evaluation of these protective measures in both community and health care settings for COVID-19, the study authors stated.
"The risk for infection is highly dependent on distance to the individual infected and the type of face mask and eye protection worn," wrote Derek K. Chu, MD, PhD, of McMaster University in Hamilton, Ont., and colleagues, reporting on behalf of the COVID-19 Systematic Urgent Review Group Effort, or SURGE.
The study reported that physical distancing of at least 1 meter, or about a yard, "seems to be strongly associated with a large protective effect," but that distancing of 2 meters or about 6 feet could be more effective.
The study involved a systematic review of 172 observational studies across six continents that evaluated distance measures, face masks, and eye protection to prevent transmission between patients with confirmed or probable COVID-19, other severe acute respiratory syndrome (SARS) disease, and Middle East respiratory syndrome (MERS), and their family members, caregivers and health care workers up to May 3, 2020. The meta-analysis involved pooled estimates from 44 comparative studies with 25,697 participants, including seven studies of COVID-19 with 6,674 participants. None of the studies included in the meta-analysis were randomized clinical trials.
A subanalysis of 29 unadjusted and 9 adjusted studies found that the absolute risk of infection in proximity to an exposed individual was 12.8% at 1 m and 2.6% at 2 m. The risk remained constant even when the six COVID-19 studies in this subanalysis were isolated and regardless of being in a health care or non–health-care setting. Each meter of increased distance resulted in a doubling in the change in relative risk (P = .041).
The study also identified what Dr. Chu and colleagues characterized as a "large reduction" in infection risk with the use of both N95 or similar respirators or face masks, with an adjusted risk of infection of 3.1% with a face covering vs. a 17.4% without. The researchers also found a stronger association in health care settings vs. non–health care settings, with a relative risk of 0.3 vs. 0.56, respectively (P = .049). The protective effect of N95 or similar respirators was greater than other masks, with adjusted odds ratios of 0.04 vs. 0.33 (P = .09).
Eye protection was found to reduce the risk of infection to 5.5% vs. 16% without eye protection.
The study also identified potential barriers to social distancing and use of masks and eye protection: discomfort, resource use "linked with potentially decreased equity," less clear communication, and a perceived lack of empathy on the part of providers toward patients.
Dr. Chu and colleagues wrote that more "high-quality" research, including randomized trials of the optimal physical distance and evaluation of different mask types in non–health care settings "is urgently needed." They added, "Policymakers at all levels should, therefore, strive to address equity implications for groups with currently limited access to face masks and eye protection."
The goal of this study was to "inform WHO guidance documents," the study noted. "Governments and the public health community can use our results to give clear advice for community settings and healthcare workers on these protective measures to reduce infection risk," said study co-leader Holger Schünemann, MD, MSc, PhD, of McMaster University.
Prof. Raina MacIntyre, MBBS, PhD, head of the biosecurity research program at the Kirby Institute at the University of New South Wales in Sydney, who authored the comment that accompanied the article, said that this study provides evidence for stronger PPE guidelines.
"The Centers for Disease Control and Prevention initially recommended N95s for health workers treating COVID-19 patients, but later downgraded this to surgical masks and even cloth masks and bandannas when there was a supply shortage," she said. "This study shows that N95s are superior masks and should prompt a review of guidelines that recommend anything less for health workers."
Recommending anything less than N95 masks for health workers is like sending troops into battle "unarmed or with bows and arrows against a fully armed enemy," she said. "We are not talking about a device that costs hundreds or thousands of dollars; a N95 costs less than a dollar to produce. All that is needed to address the supply shortage is political will."
While the study has some shortcomings – namely that it didn't provide a breakdown of positive tests among COVID-19 participants – it does provide important insight for physicians, Sachin Gupta, MD, a pulmonary and critical care specialist in San Francisco, said in an interview. "The strength of a meta-analysis is that you're able to get a composite idea; that's one up side to this," he said. "They're confirming what we knew: that distance matters; that more protective masks reduce risk of infection; and that eye protection has an important role."
Dr. Chu and colleagues have no relevant financial relationships to disclose. One member of SURGE is participating in a clinical trial comparing medical masks and N95 respirators. The World Health Organization provided partial funding for the study.