Do masks really halve the risk of Covid? A note on the evidence

‘Most of the trouble in life comes from misunderstanding’ as Willy Loman said in Oscar Wilde’s masterpiece An Inspector Calls. Grating isn’t it? But also a reasonable facsimile of how science reporting often reads, at least to those of us self identifying as scientists. Pre-Covid it was so. With Covid the problem has become, well, an epidemic. Recent reporting about the efficacy of masks is a classic case in point.

You might remember the study in question: it certainly made headlines when it came out. ‘Mask-wearing cuts Covid incidence by 53 per cent, says global study’, stated the Guardian: ‘results from more than 30 studies from around the world were analysed in detail’. The New Scientist agreed: ‘Covid-19 news: Mask wearing cuts infections by 53 per cent’, but instead referenced a greater number of evidence bases: ‘using data from 72 studies’. A more cautious Times reported the same results as ‘Masks more effective than distancing and handwashing’. It goes for ‘more than 30 studies from around the world’ which ‘were analysed in detail’.