A review by T. Jefferson et al titled “Physical interventions to interrupt or reduce the spread of respiratory viruses” found that “masks in the community probably makes little or no difference” to the outcome of influenza-like and COVID-19-like illnesses.
The entire document is 326 pages and I would be lying if I stated that I have read it all. The main body is about 35 pages long, the rest are references, data and appendices. This is partly due to the large amount of studies the review collects and analyzes.
Included are approximately 120 pages of “Characteristics of Studies” which are brief comments about the studies included and excluded in this review. Not all studies reviewed were related to COVID-19 or conducted during epidemic periods.
The Discussion on page 30 discusses the findings of 13 comparisons.
Just to mention three, when comparing medical/surgical masks to no masks, there is moderate-certainty evidence that masks make “little or no difference”.
When comparing N95 respirators to medical/surgical masks, there is low-certainty evidence to suggest the same.
Hand hygiene, however, “may offer a benefit for hand hygiene for the composite outcome ‘acute respiratory infections (ARI) or ILI or influenza’ (RR 0.89, 95% CI 0.83 to 0.94; low-certainty evidence), and probably offers a benefit for the outcomes ARI alone (RR 0.86, 95% CI 0.81 to 0.90; moderate-certainty evidence), and absenteeism (RR 0.64, 95% CI 0.58 to 0.71).”
In other words, it verifies the commonsensical view that masks don’t do jack and good hygiene like washing hands helps at least a little.
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