Do Masks Work?
A 2016
study in Beijing by MacIntyre, et al. that claimed to find a possible benefit of masks did not prove very informative, as only one person in the control group—and one in the mask group—developed a laboratory-confirmed infection. Much more illuminating was a 2010
study in France by Canini, et al., which randomly placed sick people, or “index patients,” and their household contacts together into either a mask group or a no-mask control group. The authors “observed a good adherence to the intervention,” meaning that the index patients generally wore the furnished three-ply masks as intended. (No one else was asked to wear them.) Within a week, 15.8 percent of household contacts in the no-mask control group and 16.2 percent in the mask group developed an “influenza-like illness” (ILI). So, the two groups were essentially dead even, with the sliver of an advantage observed in the control group not being statistically significant. The authors write that the study “should be interpreted with caution since the lack of statistical power prevents us to draw formal conclusion regarding effectiveness of facemasks in the context of a seasonal epidemic.” However, they state unequivocally, “In various sensitivity analyses, we did not identify any trend in the results suggesting effectiveness of facemasks.”
With the two RCTs that directly tested source control providing essentially no support for the claim that wearing a mask benefits others, what about RCTs that test the combination of source control and wearer protection? By dividing participants into a hand-hygiene group, a hand-hygiene group that also wore masks, and a control group, three RCTs allow us to see whether the addition of masks (worn both by the sick person and others) provided any benefit over hand hygiene alone.
A 2010
study by Larson, et al. in New York found that those in the hand-hygiene group were less likely to develop any symptoms of an upper respiratory infection (42 percent experienced symptoms) than those in the mask-plus-hand-hygiene group (61 percent). This statistically significant finding suggests that wearing a mask actually undermines the benefits of hand hygiene.