Ross Clark Ross Clark

Do masks really slash the risk of catching Covid?

(Getty)

Which public health interventions help to cut the spread of Covid-19 — and which do not? Except for vaccinations, where we have extensive trial data, this is a question on which the government has had little information to help it. But this morning’s headlines appear to offer an answer: wearing masks may help slash Covid infections by 53 per cent. Unfortunately, what the headlines don’t tell us is what kind of mask-wearing, where and in which circumstances. Do we need surgical grade masks or will cloth do? Should we wear them in the street or just indoors? Can we take them off if travelling in a near-empty train carriage?

The headlines are based on a paper led by Monash University in Australia and published in the British Medical Journal, which reviews 72 studies that have each tried to quantify public health interventions. But the details provide a far murkier answer than the headlines would imply — and still leave us largely in the dark.

Perhaps those who actively choose to wear masks are especially careful

Three main interventions were assessed: handwashing, mask-wearing and physical distancing. With handwashing, three studies were assessed, involving a total of 10,345 people (292 of whom contracted Covid during the study period). Merging the results, handwashing appeared to reduce the incidence of infection by 53 per cent — although the researchers said this was not statistically significant.

Six studies assessed mask-wearing, involving a total of 389,228 people (2,627 of whom contracted Covid). This found that mask-wearers were also 53 per cent less likely to be infected — but this time, the Monash team deemed the results significant. The studies also produce varying results, with mask-wearers’ relative risk of catching Covid ranging from 21 per cent to 82 per cent.

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