Revisiting the evidence for physical distancing, face masks, and eye protection
Authors: Willem Marten Lijfering
Journal: The Lancet (2021)

Derek Chu and colleagues' 2020 meta-analysis1Chu DK Akl EA Duda S et al.Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis.Lancet. 2020; 395: 1973-1987Summary Full Text Full Text PDF PubMed Scopus (2744) Google Scholar 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.1Chu DK Akl EA Duda S et al.Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis.Lancet. 2020; 395: 1973-1987Summary Full Text Full Text PDF PubMed Scopus (2744) Google Scholar 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.2Wang X Pan Z Cheng Z Association between 2019-nCoV transmission and N95 respirator use.J Hosp Infect. 2020; 105: 104-105Summary Full Text Full Text PDF PubMed Scopus (137) Google Scholar In that study,2Wang X Pan Z Cheng Z Association between 2019-nCoV transmission and N95 respirator use.J Hosp Infect. 2020; 105: 104-105Summary Full Text Full Text PDF PubMed Scopus (137) Google Scholar 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-2.2Wang X Pan Z Cheng Z Association between 2019-nCoV transmission and N95 respirator use.J Hosp Infect. 2020; 105: 104-105Summary Full Text Full Text PDF PubMed Scopus (137) Google Scholar 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 Article1Chu DK Akl EA Duda S et al.Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis.Lancet. 2020; 395: 1973-1987Summary Full Text Full Text PDF PubMed Scopus (2744) Google Scholar (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".3Tressoldi PE Extraordinary claims require extraordinary evidence: the case of non-local perception, a classical and Bayesian review of evidences.Front Psychol. 2011; 2: 117Crossref PubMed Scopus (37) Google Scholar 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. I declare no competing interests.