Physical Distancing, Face Masks, and Eye Protection to Prevent Transmission of COVID-19

Evidence for physical distancing, face masks, and eye protection.

Many of us watched in horror over the Memorial Day weekend while multitudes wantonly abandoned social distancing and masking and as states backed away from closures and imposition of nonpharmaceutical interventions (NPIs). Now, two weeks later—as experts predicted—we are seeing a significant rise in COVID-19 cases across the United States. This phenomenon brought back a passage from my favorite treatise of the 1918 influenza pandemic:

“Studying the record of the American people in 1918 and 1919 is like standing on a high hill and watching a fleet of many vessels sailing across a current of terrible power to which the sailors pay little attention. They grip their tillers firmly, peer at their compasses, and hold faithfully to courses, which, from their vantage, seem to be straight, but we can see that the secret current is sweeping them far downstream. The immense flow swamps many of the ships and their sailors drown, but the others take little notice. The other are intent on maintaining their own unwavering courses.”¹

In this rapidly evolving pandemic, and in the absence of preventive vaccines and routinely available and effective therapeutics, it is incredibly important to assess the evidence for or against the use of three easily available NPIs: physical distancing, face masks, and eye protection. A recent systematic review and meta-analysis does just that, providing significant support for these public health measures.²

The authors identified 172 observational studies for the systematic review and a subset of 44 comparative studies for the meta-analysis. As with many of our public health interventions, no randomized controlled studies were available. I think the most important findings are summarized in the GRADE (Grading of Recommendations Assessment, Development and Evaluation) table:

• A physical distance of more than 1 meter probably results in a large reduction in virus infection; for every 1 meter further away in distancing, the relative effect might increase 2.02 times.
  • The adjusted odds ratio (aOR: ≥1 m vs < 1 m) = 0.18 [95% CI: 0.09—0.38)
  • GRADE level of certainty: moderate
  • CDC currently recommends 6 feet (~2 m)
• Medical or surgical face masks might result in a large reduction in virus infection; N95 respirators might be associated with a larger reduction in risk compared with surgical or similar masks.
  • aOR (face mask vs no mask) = 0.15 [0.07—0.34]
  • GRADE level of certainty: low
• Eye protection might result in a large reduction in virus infection.
  • Unadjusted risk ratio (faceshield or goggles vs no eye protection) = 0.34 [0.22—0.52]
  • GRADE level of certainty: low

Bottom line for clinicians: NPIs work. We do not know how well they work in combination with each other. We do not have high-quality randomized controlled trials. We do, however, have substantial evidence, and for now NPIs are all we have.

References

1. Crosby AW. America’s Forgotten Pandemic: The Influenza of 1918 (New Edition). Cambridge University Press. 2003.
2. Chu DK, Akl EA, Duda S et al., on behalf of the COVID-19 Systematic Urgent Review Group Effort (SURGE) study authors. Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis. www.thelancet.com Published online June 1, 2020 https://doi.org/10.1016/S0140-6736(20)31142-9.