Eight key questions on the Danish facemask study

The ‘Danmask-19 trial‘ sought to test whether face masks are effective in preventing infection with SARS-CoV-2 (the virus that causes Covid-19) for the wearer. It found that the recommendation to wear surgical masks to supplement other public health measures ‘did not reduce the SARS-CoV-2 infection rate among wearers by more than half in a community’. So does this mean wearing masks is a waste of time? There are several reasons that drawing such a conclusion from this study might be unwise.

A randomised controlled trial (RCT) is often – though not always – the best way of testing whether a treatment works, because RCTs guard against the biases inherent in many other research designs. But RCTs can be designed to answer mission-critical questions or more marginal ones, and they can be done more or less rigorously. Here are eight questions to ask about the study:

Why did the trial focus on protecting the wearer?

‘Does my mask protect me?’ is a legitimate scientific question.