Face Masks Are Useless, Unless You're A Bank Robber

In this post from yesterday I asked where the studies were that showed face mask use is effective against the 'rona.  Just this morning I read about a study from Denmark:

Do face masks work? Last week, Gov. Doug Burgum of North Dakota decided that masks could play a significant role in stopping COVID-19 and made masks mandatory in a number of public places. Iowa soon followed suit, bringing the total number of states with mask mandates to 36. But are these policies backed by the scientific evidence?

Wednesday marked the publication of a long-delayed trial in Denmark which hopes to answer that very question. The ‘Danmask-19 trial’ was conducted in the spring with over 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...

But overall, there is a troubling lack of robust evidence on face masks and COVID-19. There have only been three community trials during the current pandemic comparing the use of masks with various alternatives — one in Guinea-Bissau, one in India and this latest trial in Denmark. The low number of studies into the effect different interventions have on the spread of COVID-19 — a subject of global importance — suggests there is a total lack of interest from governments in pursuing evidence-based medicine...

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...

But observational studies are prone to recall bias: in the heat of a pandemic, not very many people will recall if and when they used masks and at what distance they kept from others. The lack of random allocation of masks can also ‘confound’ the results and might not account for seasonal effects. A recent observational study paper had to be withdrawn because the reported fall in infection rates over the summer was reverted when the seasonal effect took hold and rates went back up.

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. Many people have argued that it is too difficult to wait for randomized trials — but Danmask-19 has shown that these kind of studies are more than feasible.

So what did the Danmask study show?

Around half of those in the trial received 50 disposable surgical face masks, which they were told to change after eight hours of use. After one month, the trial participants were tested using both PCR, antibody and lateral flow tests and compared with the trial participants who did not wear a mask.

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. Of those wearing masks, 1.8 percent caught COVID, compared to 2.1 percent 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 percent 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 percent of this group were also infected.

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.

Science would indicate that you follow the data, not your own intuition.  What do the data tell us?