The debate over masks’ effectiveness in fighting the spread of the coronavirus intensified recently when a respected scientific non-profit said its review of studies assessing measures to impede the spread of viral illnesses found it was “uncertain whether wearing masks or N95/P2 respirators helps to slow the spread of respiratory viruses.”
Now the organisation, Cochrane, says the way it summarised the review was unclear and imprecise, and that the way some people interpreted it was wrong.
“Many commentators have claimed that a recently updated Cochrane review shows that ‘masks don’t work’, which is an inaccurate and misleading interpretation,” Karla Soares-Weiser, the editor-in-chief of the Cochrane Library, said in a statement.
“The review examined whether interventions to promote mask wearing help to slow the spread of respiratory viruses,” Soares-Weiser said, adding, “Given the limitations in the primary evidence, the review is not able to address the question of whether mask wearing itself reduces people’s risk of contracting or spreading respiratory viruses.”
She said that “this wording was open to misinterpretation, for which we apologise,” and that Cochrane would revise the summary.
Soares-Weiser also said, though, that one of the lead authors of the review even more seriously misinterpreted its finding on masks by saying in an interview that it proved “there is just no evidence that they make any difference.” In fact, Soares-Weiser said, “that statement is not an accurate representation of what the review found.”
Cochrane reviews are often referred to as gold standard evidence in medicine because they aggregate results from many randomised trials to reach an overall conclusion — a great method for evaluating drugs, for example, which often are subjected to rigorous but small trials. Combining their results can lead to more confident conclusions.
Masks and mask mandates have been a hot controversy during the pandemic. The flawed summary — and further misinterpretation of it — set off a debate between those who said the study showed there was no basis for relying on masks or mask mandates and those who said it did nothing to diminish the need for them.
Michael D Brown, a doctor and academic who serves on the Cochrane editorial board and made the final decision on the review, told me the review couldn’t arrive at a firm conclusion because there weren’t enough high-quality randomised trials with high rates of mask adherence.
While the review assessed 78 studies, only 10 of those focused on what happens when people wear masks versus when they don’t, and a further five looked at how effective different types of masks were at blocking transmission, usually for health care workers. The remainder involved other measures aimed at lowering transmission, like hand washing or disinfection, while a few studies also considered masks in combination with other measures. Of those 10 studies that looked at masking, the two done since the start of the Covid-19 pandemic both found that masks helped.
The calculations the review used to reach a conclusion were dominated by pre-pandemic studies that were not very informative about how well masks blocked the transmission of respiratory viruses.
For example, in one study of haj pilgrims in Mecca, only 24.7 per cent of those assigned to wear masks reported using one daily, but not all the time (while 14.3 per cent in the no-mask group wore one anyway). The pilgrims then slept together, generally in tents with 50 or 100 people. Not surprisingly, given there was little difference between the two groups, researchers found no difference from mask wearing and declared their results “inconclusive.”
In another pre-pandemic study, college students were asked to wear masks for at least six hours a day while in their dormitories, but they were not obligated to wear them elsewhere.
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