Given the importance of this topic, some points are worth discussing.

First, even if masks don’t do much to protect wearers, as this study suggests, they can protect other people from infected wearers.^[1]^[2]

Second, this study involved a mix of people (some wearing masks, some not wearing masks) in an area where wearing masks wasn’t compulsory. It didn’t include a mix of areas (some where wearing masks was compulsory, some where wearing masks wasn’t compulsory). It’s possible that a higher percentage of mask wearers living in one area would decrease transmission rates. For example, wearing a mask in a grocery store may be less effective if many other shoppers aren’t wearing masks.

Third, at the time of this study, Denmark’s total case count was declining and the country was under lockdown, so this study primarily shows that masks didn’t measurably benefit wearers living in an area on lockdown and with a low baseline risk of infection.

Fourth, the authors determined the study’s necessary sample size under the assumption that mask wearing reduces disease transmission by 50%. It’s not clear how much masks actually reduce transmission, but it might not be by this much. Yet even a 10–20% reduction in transmission would have a massive effect at a population-wide level. If the benefit of mask over no mask is smaller than the authors assumed, the study could be far too small to actually detect a difference, especially given the fairly small number of people who got infected during the study.

Latest mask study disappoints, but with important caveats Original paper