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Top journal retracts study claiming masks ineffective in preventing COVID-19 spread

One of the world’s leading medical journals has retracted a widely circulated paper published in April that concluded that “both surgical and cotton masks seem to be ineffective in preventing the dissemination of SARS–CoV-2 from the coughs of patients with COVID-19 to the environment and external mask surface.”

The study, published by the Annals of Internal Medicine, has been cited by dozens of news stories, nearly 10,000 Twitter users — some of whom raised red flags about its methods — and by the World Health Organization.

But it turns out that the authors failed to consider the limits of the test they were using to detect the presence of coronavirus.

The paper only involved four participants. Apparently, the authors thought a correction — adding more patients — would be enough:

According to recommendations by the editors of Annals of Internal Medicine, we are retracting our article, “Effectiveness of Surgical and Cotton Masks in Blocking SARS-CoV-2. A Controlled Comparison in 4 Patients,” which was published on on 6 April 2020 (1).

We had not fully recognized the concept of limit of detection (LOD) of the in-house reverse transcriptase polymerase chain reaction used in the study (2.63 log copies/mL), and we regret our failure to express the values below LOD as “<LOD (value).” The LOD is a statistical measure of the lowest quantity of the analyte that can be distinguished from the absence of that analyte. Therefore, values below the LOD are unreliable and our findings are uninterpretable. Reader comments raised this issue after publication. We proposed correcting the reported data with new experimental data from additional patients, but the editors requested retraction.

The article joins our ever-growing list of retracted COVID-19 studies. It is a reminder that for all of the alarm over publicity of preprints, because they are not peer-reviewed, “Peer-Reviewed Studies Also Require Caution.” 

Perhaps the real problem is speed, not peer-review status. If only someone had warned us.

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(Source:; June 1, 2020;
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