“…there are no rigorous studies showing masks to be an effective method of viral infection control. In fact the highest-quality scientific studies, randomised controlled trials (RCTs), show the opposite: that masks make little to no difference in controlling spread of influenza, SARS-CoV-2, or RSV.
In May 2020, the CDC summarised data from 14 RCTs as failing to show a significant benefit of masks in reducing transmission of influenza. An analysis of nine trials conducted by Cochrane, an organisation that conducts large reviews of health-care interventions, reached similar conclusions in November 2020. Studies of masking to prevent common colds and RSV also had negative results.
For Covid-19, there are two RCTs evaluating masks’ ability to cut viral spread. One, conducted in Denmark in the spring of 2020, found no statistically significant difference in infection rates between masked and unmasked groups. Another, bigger, RCT — conducted in Bangladesh from late 2020 until the following spring — showed a small but statistically significant reduction of symptomatic Covid-19 cases in villages using surgical masks. Yet even this small benefit was lost upon reanalysis using different statistical parameters. An additional finding that mask colour made a difference in effectiveness further suggests that this positive data were skewed in some way.
Another rigorous study, though not an RCT, was conducted in schools in Catalonia, Spain. This showed that unmasked five-year-olds had similar Covid-19 case rates to masked six-year-olds, the age at which masking was mandated.
These high-quality studies are noticeably not linked in any “mask up” articles. Instead, links (if any are provided) reference low-quality observational studies such as a CDC analysis from 2021 that found higher paediatric Covid-19 rates in unmasked schools compared to masked ones. This study was subsequently debunked upon reanalysis using more districts and a longer time period.
A recent analysis conducted in Massachusetts schools, reporting that masks reduced Covid-19 case rates, is another popular source used to support media exhortations to mask up. However, this study was also riddled with issues, such as changes in testing practices after masking was dropped (impacting Covid-19 detection) and differences in levels of natural immunity between masked and unmasked schools before and during the study period. In addition, many of the schools cited as requiring masks during the study period had already dropped their mandate.”
Dr Leslie Bienen, Dr Jeanne Noble and Dr Margery Smelkinson.
Dr Leslie Bienen works in health care policy. Dr Jeanne Noble is an emergency physician and director of Covid Response at the UCSF Parnassus Emergency Department. Dr Margery Smelkinson is an infectious-disease scientist whose research has focused on influenza and SARS-CoV-2.
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