Effectiveness of Adding a Mask Recommendation to Other Public Health Measures
Authors: Brendan Moran
Journal: Annals of Internal Medicine (2021)

LettersAugust 2021Effectiveness of Adding a Mask Recommendation to Other Public Health MeasuresFREEBrendan Moran, MBBS BScBrendan Moran, MBBS BScOne HMG Healthline, Esher, United KingdomSearch for more papers by this authorAuthor, Article, and Disclosure Informationhttps://doi.org/10.7326/L21-0396 SectionsAboutVisual AbstractPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinkedInRedditEmail TO THE EDITOR: Bundgaard and colleagues' study (1) pooled participants from 2 cohorts split 2 weeks apart in the months after the peak of the first wave of SARS-CoV-2 infections in Denmark. The self-reported prestudy baseline prevalence of seropositivity was 1.7%, and these seropositive participants were excluded from the study. Among those with unknown baseline seropositivity, 2% were seropositive at the end of the study. Among those with known baseline seropositivity, approximately 1.7% seem to have seroconverted during the study month. Should these similar percentages spread across a period of falling infection rates raise concerns about the self-reporting false-positive rate of the antibody test when used in a low-prevalence population?Even without a false-positive rate, this lateral flow antibody test must be performed at least 15 days after symptom onset to achieve 80% sensitivity. It takes an average of 5 to 6 days to develop symptoms after exposure, which creates a lag of 3 weeks. Because Bundgaard and colleagues' study lasted only 1 month for each cohort, any protective effect of mask wearing would be diluted by late seroconversions in participants infected before the study. This effect would be balanced in the control group; however, it would still increase the odds ratio toward 1 even if masks had an effect. Accounting for this and any poststudy seroconversions missed in the control group may have led to a statistically significant result.The polymerase chain reaction assay and clinically diagnosed outcomes will not be affected much from this lag. Of note, 0 and 5 cases were identified by polymerase chain reaction assay and clinical diagnosis, respectively, versus 5 and 10 cases for control participants. In addition, IgG seropositivity was higher than IgM seropositivity in mask wearers; the opposite was true in control participants.Furthermore, the study was underpowered for detecting a protective-to-wearer effect of somewhere less than 50%, which could be a more reasonable estimate of efficacy.Reference1. Bundgaard H, Bundgaard JS, Raaschou-Pedersen DET, et al. Effectiveness of adding a mask recommendation to other public health measures to prevent SARS-CoV-2 infection in Danish mask wearers. A randomized controlled trial. Ann Intern Med. 2021;174:335-43. [PMID: 33205991]. doi:10.7326/M20-6817 LinkGoogle Scholar Comments0 CommentsSign In to Submit A Comment Author, Article, and Disclosure InformationAffiliations: One HMG Healthline, Esher, United KingdomDisclosures: The author has reported no disclosures of interest. The form can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=L21-0396. PreviousarticleNextarticle Advertisement FiguresReferencesRelatedDetailsSee AlsoEffectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers Henning Bundgaard , Johan Skov Bundgaard , Daniel Emil Tadeusz Raaschou-Pedersen , Christian von Buchwald , Tobias Todsen , Jakob Boesgaard Norsk , Mia M. Pries-Heje , Christoffer Rasmus Vissing , Pernille B. Nielsen , Ulrik C. Winsløw , Kamille Fogh , Rasmus Hasselbalch , Jonas H. Kristensen , Anna Ringgaard , Mikkel Porsborg Andersen , Nicole Bakkegård Goecke , Ramona Trebbien , Kerstin Skovgaard , Thomas Benfield , Henrik Ullum , Christian Torp-Pedersen , and Kasper Iversen Effectiveness of Adding a Mask Recommendation to Other Public Health Measures Matthew A. Spinelli , David V. Glidden , Efstathios D. Gennatas , George W. Rutherford , and Monica Gandhi Effectiveness of Adding a Mask Recommendation to Other Public Health Measures Hans Gaines Effectiveness of Adding a Mask Recommendation to Other Public Health Measures Carl Llor Effectiveness of Adding a Mask Recommendation to Other Public Health Measures Janet Rand Effectiveness of Adding a Mask Recommendation to Other Public Health Measures Henning Bundgaard , Anna K. Ringgaard , Daniel Emil Tadeusz Raaschou-Pedersen , Johan Skov Bundgaard , and Kasper K. Iversen Metrics August 2021Volume 174, Issue 8Page: 1192-1193 ePublished: 17 August 2021 Issue Published: August 2021 Copyright & PermissionsCopyright © 2021 by American College of Physicians. All Rights Reserved.PDF downloadLoading ...