ARGUMENT: Face-mask effect Landmark Danish Study Shows Face Masks Have No Significant Effect

Published 21 November 2020

Do face masks work? Carl Heneghan and Tom Jefferson write that a just-published study reports the results of a trial in Denmark – a study which hopes to answer that very question. “In the end, there was no statistically significant difference between those who wore masks and those who did not when it came to being infected by Covid-19,” they write.

Do face masks work? Earlier this year, the U.K. government decided that masks could play a significant role in stopping Covid-19 and made masks mandatory in a number of public places. But are these policies backed by the scientific evidence?

Carl Heneghan and Tom Jefferson write in The Spectator that a just-published study reports the results of a trial in Denmark – a study which hopes to answer that very question. The ‘Danmask-19 trial’ was conducted in the spring with more than 3,000 participants, when the public were not being told to wear masks but other public health measures were in place. Unlike other studies looking at masks, the Danmask study was a randomized controlled trial – making it the highest quality scientific evidence.

In the end, there was no statistically significant difference between those who wore masks and those who did not when it came to being infected by Covid-19. 1.8 per cent of those wearing masks caught Covid, compared to 2.1 per cent of the control group. As a result, it seems that any effect masks have on preventing the spread of the disease in the community is small.

Some people, of course, did not wear their masks properly. Only 46 per cent of those wearing masks in the trial said they had completely adhered to the rules. But even if you only look at people who wore masks ‘exactly as instructed’, this did not make any difference to the results: 2 per cent of this group were also infected.

When it comes to masks, it appears there is still little good evidence they prevent the spread of airborne diseases. The results of the Danmask-19 trial mirror other reviews into influenza-like illnesses. Nine other trials looking at the efficacy of masks (two looking at healthcare workers and seven at community transmission) have found that masks make little or no difference to whether you get influenza or not.

But overall, there is a troubling lack of robust evidence on face masks and Covid-19.

Heneghan and Jefferson note that the only trials which have shown masks to be effective at stopping airborne diseases have been ‘observational studies’ – which observe the people who ordinarily use masks, rather than attempting to create a randomized control group.

This is why large, randomized trials like this most recent Danish study are so important if we want to understand the impact of measures like face masks…. And now that we have properly rigorous scientific research we can rely on, the evidence shows that wearing masks in the community does not significantly reduce the rates of infection.

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