A recent study of wearing masks in Denmark is shared as if to prove that masks do not protect us. It’s not really said in the study.
I will go into the details below, but for now I would like to point out a few lines from the document itself:
The most important limitation is that the findings are unconvincing …
It is important to emphasize that this study does not consider the effects of masks as a source control [protecting others from the wearer] or as protection in conditions where social distancing and other public health measures are not in force.
So, if you share this study to support your opinion that masks are stupid and you do not want to wear them, please stop. Now let’s see what the study was really about.
What question is the study intended to answer?
The newly published study, entitled Effectiveness of adding a mask recommendation to other public health measures to prevent SARS-CoV-2 infection in Danish mask wearers, was held in Denmark in April and May this year.
The setting of the study was not much like the world we live in now. There were few cases and most people did not wear masks. The country relied on social distancing as their main way to slow the spread of COVID-19, with a blockade that began in March and continued in May.
The question was: if we send people a box of masks and tell them to wear them, will people with masks have a drastically reduced risk of infection? The study was not blinded, because you obviously know if you are wearing a mask. Participants were tested for antibodies and reported in a study whether they wore the masks according to the instructions.
What did they find?
Investigators did not see the drastic reduction in infection they had hoped for. Both groups – those who were sent a box of masks and those who were not – ended up with approximately similar levels of infection.
Did they see a small risk reduction? It is impossible to say. The study was driven, in a statistical senseto detect a 50% reduction in infections between the mask group and the control group. If the masks reduce the risk by a lower size – 25%? 10%? – the study failed to find this.
Therefore, the main finding of the study was reported to be from less than 50% reduction to possible even increase in infection. This is a large set of possibilities, as the study was not designed to reveal the difference between any of them.
“At the bottom – wearing a mask is unlikely to halve the risk of infection. But it could reduce it by 20%, and in an entire country experiencing a massive epidemic, that’s adding, “said epidemiologist Gideon Mayerowitz-Katz of the University of Wollongong.
What did not find
The study does not ask what happens if most people around you are wearing masks and you decide not to. (Wearing a mask was unusual in Denmark at the time.)
The study does not ask what happens if you are busy with your life, shopping and communicating without a mask. (Denmark was locked up for most of the study.)
The survey does not test the mandate for a mask across the country (again, there was none).
The study does not test whether masks prevent you from spreading the coronavirus if you are ill. (It only considered the risk of infection for the user.)
The study does not directly test masks, but only what happens when you advise people to wear them. (Like Vinay Prasad wrote in MedPage today, “The cake is both the dough and the oven temperature, and the public health recommendation is both the recommendation itself and whether people follow it.” This study does not separate the two.)
As the CDC recently clarified, we have other evidence that the masks are likely to benefit the consumer. The Danish study complements our knowledge by telling us not to expect masks to be of great benefit to the consumer. He also reminds us that people do not always follow recommendations; study participants had to report whether they wore the masks as recommended, and only about half said they followed the instructions exactly.
“It is not correct to say that masks have failed or are useless based on this study,” says Meyerowitz-Katz. He points out that the mandates of masks can still have “great benefits for society”, even if the benefits for each individual are small. We already knew that, didn’t we? Keep wearing your mask.