3 feet of social distancing could cut coronavirus risk but 6 feet is more effective: Study
Keeping a distance of at least one meter or 3 feet from other people as well as wearing face coverings and eye protection, in and outside of healthcare settings, could be the best way to reduce the chance of viral infection or transmission of Covid-19, according to a new analysis. But none of these interventions, even when properly used and combined, give complete protection from infection, said researchers from multiple institutions.
The research team found that keeping a distance of over one meter (over 3 feet) from other people was associated with a much lower risk of Covid-19 infection compared with less than one meter (less than 3 feet). The risk of infection when individuals stand more than a meter away from the infected individual was 2.6% versus 12.8% if less than a meter. However, the modeling suggests that for every extra meter further away up to three meters, the risk of infection or transmission may halve. "From a policy and public health perspective, current policies of at least 1-meter physical distancing seem to be strongly associated with a large protective effect, and distances of 2 meter (6 feet) could be more effective. Hence, the results of our current review support the implementation of a policy of physical distancing of at least 1 meter and, if feasible, 2 meters or more," said researchers in their findings published in The Lancet.
Many countries and regions have issued conflicting advice about physical distancing to reduce transmission of Covid-19, based on limited information. In addition, the questions of whether masks and eye coverings might reduce transmission of Covid-19 in the general population, and what the optimum use of masks in healthcare settings is, have been debated during the pandemic. "Our findings are the first to synthesize all direct information on COVID-19, SARS, and MERS, and provide the currently best available evidence on the optimum use of these common and simple interventions to help flatten the curve and inform pandemic response efforts in the community. 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," says Professor Holger Schünemann from McMaster University in Canada, who co-led the research, in the analysis.
The study is the first review of all available evidence, including 172 observational studies, looking at how physical distancing, face masks and eye protection affect the spread of Covid-19, SARS and MERS across 16 countries. Pooled estimates from 44 comparative studies involving 25,697 participants were included in the meta-analysis. Of these, seven studies focused on Covid-19 (6,674 participants), 26 on SARS (15,928) and 11 on MERS (3,095). According to the researchers, the study, partly funded by World Health Organization (WHO) and conducted to inform WHO guidance documents, have systematically examined the optimum use of protective measures in both community and healthcare settings for Covid-19. The authors say it has immediate and important implications for curtailing the current coronavirus pandemic and future waves by informing disease models and standardizing the definition of who has been 'potentially exposed' (that is, within 2 meters) for contact tracing.
According to the analysis, 13 studies (across all three viruses, including 3,713 participants) focusing on eye protection found that face shields, goggles and glasses were associated with a lower risk of infection, compared with no eye covering. The risk of infection or transmission when wearing eye protection was 5.5% versus 16% when not wearing eye protection. The authors note that the certainty of the evidence for eye coverings is low. Evidence from 10 studies (across all three viruses, including 2,647 participants) also found similar benefits for face masks in general. The risk of infection or transmission when wearing a mask was 3% versus 17% when not wearing a mask. Evidence in the study was looking mainly at mask use within households and among contacts of cases, and was also based on evidence of low certainty, say experts.
For healthcare workers, N95 and other respirator-type masks might be associated with greater protection from viral transmission than surgical masks or similar (for example, reusable 12-16 layer cotton or gauze masks). For the general public, face masks are also probably associated with protection, even in non-healthcare settings, with either disposable surgical masks or reusable 12-16 layer cotton ones. However, the authors note that there are concerns that mass face mask use risks diverting supplies from healthcare workers and other caregivers who are at the highest risk for infection.
The research team emphasizes that policymakers will need to quickly address access issues for face masks to ensure that they are equally available for all. "With respirators such as N95s, surgical masks, and eye protection in short supply, and desperately needed by healthcare workers on the front lines of treating Covid-19 patients, increasing and repurposing of manufacturing capacity is urgently needed to overcome global shortages," says co-author Dr Derek Chu, assistant professor at McMaster University, in the analysis. "We also believe that solutions should be found for making face masks available to the general public. However, people must be clear that wearing a mask is not an alternative to physical distancing, eye protection, or basic measures such as hand hygiene, but might add an extra layer of protection," added Dr Chu.
Writing in a linked comment, Professor Raina MacIntyre (who was not involved in the study) from the Kirby Institute, University of New South Wales in Australia, describes the study as "an important milestone". She says that the study should prompt a review of all guidelines that recommend a medical mask for health workers caring for Covid-19 patients. “Although medical masks do protect, the occupational health and safety of health workers should be the highest priority and the precautionary principle applied,” she says. “(They) also report that respirators and multilayer masks are more protective than are single layer masks. This finding is vital to inform the proliferation of homemade cloth mask designs, many of which are single-layered. A well-designed cloth mask should have water-resistant fabric, multiple layers and good facial fit. Universal face mask use might enable safe lifting of restrictions in communities seeking to resume normal activities and could protect people in crowded public settings and within households,” says MacIntyre.