A meta-analysis of 172 studies on coronavirus transmission recently published in The Lancet showed that social distancing of at least one meter and using face masks corresponded with a sizable reduction in risk of infection from SARS-CoV-2. The data also suggests that N95 masks or similar respirators may be associated with more protection from viral infection than disposable surgical masks or reusable cotton masks, but the authors noted that more data was needed to be certain.
The report, funded by the World Health Organization (WHO), looked at observational studies from 16 countries that were conducted during the COVID-19 pandemic, as well as studies from the earlier SARS and MERS epidemics, including data from 25,697 patients. The report is among the first to explore transmission data specific to coronaviruses, as opposed to extrapolating from data on other respiratory viruses.
Rates of infection were lower with physical distancing of at least 1 meter, compared with distancing of less than 1 meter, or 2.6% versus 12.8% respectively. Protection increased around 2.02% per meter of additional physical distance. The results were similar regardless of causative virus, health-care setting versus non-health-care setting, or type of face mask worn.
The use of face masks in general was also associated with lower rates of transmission for those exposed to infected individuals, or 3.1% compared to 17.4% with no face mask. Stronger associations were found in healthcare settings compared with non-health-care settings. Protection was more substantial with the use of N95 or other respirators, with respirators offering 96% protection compared to 73% for disposable surgical masks or reusable multilayer cotton masks.
Eye coverings like face shields and goggles were also found to provide additional protection against transmission, with an absolute risk of 5.5% with eye protection versus 16% with no eye protection. Many studies included reported on bundled interventions, or a combination of PPE and distancing, which was addressed with statistical adjustment. The authors emphasized that people should also continue to wash their hands frequently.
Participants from the studies conducted in health-care settings reported physical distancing and using face masks and eye protection was acceptable, feasible, and reassuring, but challenges included frequent discomfort, high resource use linked with potentially decreased equity, less clear communication, and perceived reduced empathy of care providers by their patients.