Derek Chu and colleagues’ 2020 meta-analysis1 was epidemiologically flawed. In a comparison of countries where face mask wearing was mandatory (eg, China) with countries where it was not (eg, Italy), they find a lower rate of COVID-19 in countries where masks were mandatory.1 Many variables can explain such a finding, so it is clearly a case of correlation not causation. The only country-wide study included in the meta-analysis that investigated whether face mask wearing protects against COVID-19 was from China.2 In that study,2 health-care workers’ risk of COVID-19 in hospital departments where face masks were mandatory was compared against the risk to health-care workers in hospital departments where masks were not mandatory. None of the personnel who wore face masks became infected with SARS-CoV-2, whereas ten individuals in departments were masks were not mandatory were infected with SARS-CoV-2.2 Should one consider whether these results are unbiased and true, then the evidence of wearing face masks comes from a study where only ten people had the outcome of interest.
Since the political effects that might be taken from the conclusions are to impose a measure to wear face masks on billions of people worldwide, we can surely say that there is an absence of evidence here.
The authors claim that their meta-analysis has no bias because they run a lot of models. However, a funnel plot analysis in the appendix to the Article1 (not discussed in the Article) clearly shows no symmetry—ie, a gap in the right side pushing the results towards an effect that face masks protect against COVID-19.
Carl Sagan once said “extraordinary claims require extraordinary evidence”.3 Such evidence was not presented, and the conclusions only muddied the waters as to whether face mask wearing protects against viral respiratory diseases, a claim that not even manufacturers of face masks dare to make.
© 2021 Sumit Saraswat/Pacific Press/LightRocket/Getty Images
I declare no competing interests.
References
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