Why deniers misunderstand the Cochrane study on face masks

A review of studies by the prestigious Cochrane association supposedly indicates that masks are of little or no use in the fight against covid, but the document does not allow reaching that conclusion.

Since the beginning of the Covid-19 pandemic, there has been a lot of controversy about the usefulness of masks, which are still mandatory in some spaces in Spain, but not for much longer. At the same time around the world the requirement for masks on trains and buses and trains is being removed, a study conducted by the renowned Cochrane Research Network is causing a stir, as it seems to confirm the arguments of mask detractors. But it’s not that simple.

Deniers argue that the Cochrane study shows masks provide little or no protection against coronavirus infection. But such an interpretation of the document is wrong. In the Cochrane document, the authors bring together all the results of studies on the effectiveness of non-pharmacological measures such as quarantine, hand washing and the use of masks.

The review examined a total of 78 studies, including work on the influenza virus, the Sars-CoV-2 that causes COVID-19, and the severe acute respiratory syndrome (SARS) virus. Most studies refer to classic peak times of respiratory viruses up to 2016, not the covid pandemic.

Based on the studies reviewed, the authors write that “mask use in the population likely has little or no effect on the incidence of illnesses such as influenza and covid.” However, they limit the significance of the results. “The high risk of bias, the differences in how to measure the results and the relatively low adherence during study periods make it difficult to draw firm conclusions “, they point out. According to the researchers, it is urgent to study in more detail the extent to which masks actually protect against the coronavirus. The authors also speak of gaps in research.

In simple terms, the Cochrane study measured interventions such as the provision of masks, but it is not clear if and to what extent people used them, all with mostly pre-pandemic data. Later they include an explanation of the poverty of these data:

«The observed lack of effect of the use of masks in the interruption of the spread of flu-like illnesses (ILI) or influenza/COVID-19 in our review has many potential reasons, among which are included: poor design of the studies; underpowered studies due to low viral circulation in some studies; lower adherence to the use of masks, especially among children; quality of masks used; self-contamination of the mask with your hands; lack of protection against ocular exposure to respiratory droplets (allowing a pathway for respiratory viruses to enter the nose through the tear duct); saturation of masks with saliva due to prolonged use (which favors the survival of the virus in the proteinaceous material); and possible risk-compensating behavior leading to an exaggerated sense of security”.

Eberhard Bodenschatz, aerosol researcher and director of the Max Planck Institute for Dynamics and Self-Organization in Göttingen, says: “The Cochrane study doesn’t make a lot of sense.” A big problem with the study, he says, is that it confuses different respiratory illnesses, like covid and the regular flu. “Our studies have clearly shown that masks are wonderfully physically protective,” he told the Deutsche Presse agency. They improved protection against infections by at least 10 to 100 times, he said, adding that the individual studies were not comparable.

Bodenschatz also criticized the authors: “In one sentence they write that masks don’t work, and a paragraph later they admit they really can’t say that.” That kind of communication, he said, is unfortunate.

Several scientific analyzes have long shown that masks protect against coronavirus infection. For example, a mid-2020 review study, published in the prestigious magazine «The Lancet»shows that protective masks can significantly reduce the risk of infection.

A study published at the end of 2021 in the journal “Proceedings of the National Academy of Sciences” (PNAS), in which Bodenschatz played a key role, found that masks can significantly reduce the risk of infection: If an uninfected person and an infected person wear tight-fitting FFP2 masks, the maximum risk of infection after 20 minutes is just over one in a thousand, even at the shortest distance in a room.


Physical interventions to stop or reduce the spread of respiratory viruses

Photos: Man in medical flu mask holding globe with medical mask per marco verch under Creative Commons 2.0

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