Our new normal of has become social distancing and wearing a face mask. But the question is, do these protective measures really work? The good news is that a study published in the Lancet on June 1st says they do work. It is the best study so far in the absence of randomized clinical trials.
Chu and colleagues reviewed the evidence of 44 comparative studies on SARS, Middle East respiratory syndrome (MERS), COVID19, and the coronaviruses that cause these diseases.
The authors showed a reduction in risk of 82% with a physical distance of 1 m for both healthcare and community settings. Every additional 1 m of separation more than doubled the relative protection.
They also reported that face masks and respirator masks reduced the risk of infection by 85%. Respirators masks -used by health care workers- were 96% effective and other masks were 77% effective. Eye protection resulted in a 78% reduction in infection which might occur by aerosol transmission or touching the eyes with infected hands.
They also mentioned that multilayer masks are more protective than are single layer masks. This is of interest since most homemade cloth masks are singlelayered. A well-designed cloth mask should have waterresistant fabric, multiple layers, and good facial fit.
This study supports universal face mask use. The authors reiterate that no one intervention is completely protective, and that combinations of physical distancing and face mask use are needed to mitigate the COVID19 pandemic until we have an effective vaccine.
Chu DK, Akl EA, Duda S, et al. Physical distancing, face masks, and eye protection to prevent persontoperson transmission of SARSCoV2 and COVID19: a systematic review and metaanalysis. Lancet 2020; published online June 1. https://doi.org/10.1016/S01406736(20)311429.