Update Alert 7: Masks for Prevention of Respiratory Virus Infections, Including SARS-CoV-2, in Health Care and Community Settings
Authors: Roger Chou, Tracy Dana, Rebecca Jungbauer
Journal: Annals of Internal Medicine (2022)

LettersMay 2022Update Alert 7: Masks for Prevention of Respiratory Virus Infections, Including SARS-CoV-2, in Health Care and Community SettingsFREERoger Chou, MD, Tracy Dana, MLS, Rebecca Jungbauer, DrPHRoger Chou, MDSearch for more papers by this author, Tracy Dana, MLSSearch for more papers by this author, Rebecca Jungbauer, DrPHSearch for more papers by this authorAuthor, Article, and Disclosure Informationhttps://doi.org/10.7326/L21-0783 SectionsSupplemental MaterialAboutVisual AbstractPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinkedInRedditEmail This is the seventh update alert for a living rapid review (1) on the use of masks for prevention of respiratory virus infections, including SARS-CoV-2, in health care and community settings. The first 3 updates (2–4) were monthly, after which the interval was switched to bimonthly (5, 6). After the last update (7), done through 2 June 2021, the interval was extended to biannually. For this update, searches were done from 3 June to 2 December 2021 using the same search methods as the original review. Inclusion was restricted to randomized trials and observational studies that controlled for confounders. Non–peer-reviewed studies were excluded unless they were based on data collected after February 2021, when the Delta variant emerged. The update searches identified 1554 citations. One preprint study (8) done in a health care setting and 6 studies (9–14) done in community settings (including 1 new cluster randomized trial) (9) on masks and SARS-CoV-2 infection met inclusion criteria for this update (Supplement Tables 1 to 3).Community SettingsOne new cluster randomized trial (9) and 5 new observational studies (10–14) evaluated the effects of mask use in a community setting and risk for SARS-CoV-2 infection.In previous updates, the evidence for mask use versus no use for prevention of SARS-CoV-2 infection in community settings was previously assessed as low strength favoring mask use, based on 1 prior randomized controlled trial (15) and 3 observational studies (16–18). The new randomized controlled trial was a large cluster randomized trial (>340 000 persons) designed to assess a mask promotion and distribution intervention in Bangladesh (a country with low baseline mask) (Supplement Table 1), with further randomization to surgical or cloth masks along with various other mask promotion interventions (9). Mask promotion intervention villages were associated with decreased symptomatic SARS-CoV-2 seroprevalence (adjusted prevalence ratio, 0.90 [95% CI, 0.82 to 0.995]) and prevalence of COVID-19 symptoms according to World Health Organization criteria (adjusted prevalence ratio, 0.88 [CI, 0.83 to 0.93]) (Supplement Table 5). In an analysis stratified according to mask type, the mask promotion intervention was associated with decreased symptomatic SARS-CoV-2 seroprevalence in surgical mask villages (adjusted prevalence ratio, 0.89 [CI, 0.78 to 0.997]), with no difference in cloth mask villages (adjusted prevalence ratio, 0.94 [CI, 0.78 to 1.10]). Although no statistical test for a subgroup difference was reported, the CIs of the estimates highly overlapped, suggesting no statistically significant subgroup difference. When stratified by participant age, mask use in surgical mask villages seemed to be most beneficial in those aged 60 years or older, although there was no association between older age and mask effectiveness in the cloth mask villages. The trial was rated fair quality because of the open-label design, failure to perform serologic testing in 60% of symptomatic participants (although the proportion was similar in intervention and control villages), and differential recruitment (slightly higher in mask promotion intervention compared with no intervention villages). Also, the applicability of findings to settings with higher mask use is uncertain.Five new observational studies (10–14) also provide evidence on mask use in the community and SARS-CoV-2 infection (Supplement Table 2), although all had methodological limitations, including selection and recall bias, and limited ability to control for potential confounders (Supplement Table 4). The new studies consistently found mask use associated with reduced risk for SARS-CoV-2 infection, with adjusted risk estimates ranging from 0.04 to 0.60 (Supplement Table 5). The new evidence was consistent with the previous findings favoring mask use versus no use, and the evidence was slightly strengthened from low to low–moderate, primarily based on the new randomized controlled trial (Supplement Table 6). None of the new observational studies compared mask types.Health Care SettingsPrior updates included 4 observational studies (19–22) that provided insufficient evidence to determine the effectiveness of N95 (or equivalent) respirators versus surgical masks in health care settings (Supplement Table 6); all were done before the emergence of the Delta variant. One new cohort study (Supplement Table 2) found that health care workers who primarily used FFP2 (N95 equivalent) masks had decreased risk for SARS-CoV-2 infection (adjusted hazard ratio, 0.80 [CI, 0.64 to 1.00]) or seroconversion (adjusted odds ratio, 0.73 [CI, 0.53 to 1.00]) versus health care workers who primarily used surgical masks (Supplement Table 5) (8). In a stratified analysis, the reduction in risk among mostly FFP2 mask users was statistically significant among health care workers with frequent (>20) contacts with patients with COVID-19 (adjusted hazard ratios, 0.66 [CI, 0.54 to 0.81] for SARS-CoV-2 positive polymerase chain reaction and 0.64 [CI, 0.42 to 0.97] for seroconversion). The new study had methodological limitations, including potential recall bias, and has not yet undergone peer review; in addition, most data were collected before the emergence of the Delta variant. Therefore, the strength of evidence comparing N95 respirators with surgical masks for health care workers remains insufficient because of methodological limitations, imprecision, and inconsistency across studies (Supplement Table 6).In summary, new evidence slightly strengthened the evidence of benefit of masks versus no masks in community settings to low–moderate, with no change in insufficient strength of evidence for N95 versus surgical masks in health care settings. A final update is planned for 6 months.References1. Chou R, Dana T, Jungbauer R, et al. Masks for prevention of respiratory virus infections, including SARS-CoV-2, in health care and community settings. A living rapid review. Ann Intern Med. 2020;173:542-555. [PMID: 32579379] doi:10.7326/M20-3213 LinkGoogle Scholar2. Chou R, Dana T, Jungbauer R, et al. Update alert: masks for prevention of respiratory virus infections, including SARS-CoV-2, in health care and community settings [Letter]. Ann Intern Med. 2020;173:W86. [PMID: 32687391] doi:10.7326/L20-0948 LinkGoogle Scholar3. Chou R, Dana T, Jungbauer R, et al. Update alert 2: masks for prevention of respiratory virus infections, including SARS-CoV-2, in health care and community settings [Letter]. Ann Intern Med. 2020;173:132. [PMID: 32853032] doi:10.7326/L20-1067 LinkGoogle Scholar4. Chou R, Dana T, Jungbauer R, et al. Update alert 3: masks for prevention of respiratory virus infections, including SARS-CoV-2, in health care and community settings [Letter]. Ann Intern Med. 2020;173:169. [PMID: 33105095] doi:10.7326/L20-1292 LinkGoogle Scholar5. Chou R, Dana T, Jungbauer R, et al. Update alert 4: masks for prevention of respiratory virus infections, including SARS-CoV-2, in health care and community settings [Letter]. Ann Intern Med. 2021;174:W24. [PMID: 33370171] doi:10.7326/L20-1429 LinkGoogle Scholar6. Chou R, Dana T, Jungbauer R, et al. Update alert 5: masks for prevention of respiratory virus infections, including SARS-CoV-2, in health care and community settings. Ann Intern Med. 2021;174:W47. [PMID: 33683928] doi:10.7326/L21-0116 LinkGoogle Scholar7. Chou R, Dana T, Jungbauer R. Update alert 6: masks for prevention of respiratory virus infections, including SARS-CoV-2, in health care and community settings [Letter]. Ann Intern Med. 2021;174:W68. [PMID: 34251900] doi:10.7326/L21-0393 LinkGoogle Scholar8. Haller S, Güsewell S, Egger T, et al. Use of respirator vs. surgical masks in healthcare personnel and its impact on SARS-CoV-2 acquisition—a prospective multicentre cohort study. medRxiv. Preprint posted online 1 June 2021. doi:10.1101/2021.05.30.21258080. CrossrefGoogle Scholar9. Abaluck J, Kwong LH, Styczynski A, et al. Impact of community masking on COVID-19: a cluster-randomized trial in Bangladesh. Science. 2022;375:eabi9069. [PMID: 34855513] doi:10.1126/science.abi9069 CrossrefMedlineGoogle Scholar10. Gonçalves MR, Dos Reis, Tólio RP, et al. Social distancing, mask use, and transmission of severe acute respiratory syndrome coronavirus 2, Brazil, April-June 2020. Emerg Infect Dis. 2021;27:2135-2143. [PMID: 34087090] doi:10.3201/eid2708.204757 CrossrefMedlineGoogle Scholar11. Lio CF, Cheong HH, Lei CI, et al. Effectiveness of personal protective health behaviour against COVID-19. BMC Public Health. 2021;21:827. [PMID: 33926406] doi:10.1186/s12889-021-10680-5 CrossrefMedlineGoogle Scholar12. Rebmann T, Loux TM, Arnold LD, et al. SARS-CoV-2 transmission to masked and unmasked close contacts of university students with COVID-19 - St. Louis, Missouri, January-May 2021. MMWR Morb Mortal Wkly Rep. 2021;70:1245-1248. [PMID: 34499631] doi:10.15585/mmwr.mm7036a3 CrossrefMedlineGoogle Scholar13. Sharif N, Alzahrani KJ, Ahmed SN, et al. Protective measures are associated with the reduction of transmission of COVID-19 in Bangladesh: a nationwide cross-sectional study. PLoS One. 2021;16:e0260287. [PMID: 34807962] doi:10.1371/journal.pone.0260287 CrossrefMedlineGoogle Scholar14. Sugimura M, Chimed-Ochir O, Yumiya Y, et al. The association between wearing a mask and COVID-19. Int J Environ Res Public Health. 2021;18. [PMID: 34501719] doi:10.3390/ijerph18179131 CrossrefMedlineGoogle Scholar15. 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;174:335-343. [PMID: 33205991] doi:10.7326/M20-6817 LinkGoogle Scholar16. Wang Y, Tian H, Zhang L, et al. Reduction of secondary transmission of SARS-CoV-2 in households by face mask use, disinfection and social distancing: a cohort study in Beijing, China. BMJ Glob Health. 2020;5. [PMID: 32467353] doi:10.1136/bmjgh-2020-002794 CrossrefMedlineGoogle Scholar17. Doung-Ngern P, Suphanchaimat R, Panjangampatthana A, et al. Case-control study of use of personal protective measures and risk for SARS-CoV 2 infection, Thailand. Emerg Infect Dis. 2020;26:2607-2616. [PMID: 32931726] doi:10.3201/eid2611.203003 CrossrefMedlineGoogle Scholar18. van den Broek-Altenburg EM, Atherly AJ, Diehl SA, et al.. Jobs, housing, and mask wearing: cross-sectional study of risk factors for COVID-19. JMIR Public Health Surveill. 2021;7:e24320. [PMID: 33315576] doi:10.2196/24320 CrossrefMedlineGoogle Scholar19. Piapan L, De Michieli, Ronchese F, et al. COVID-19 outbreak in healthcare workers in hospitals in Trieste, North-east Italy. J Hosp Infect. 2020;106:626-628. [PMID: 32805309] doi:10.1016/j.jhin.2020.08.012 CrossrefMedlineGoogle Scholar20. Sims MD, Maine GN, Childers KL, et al. Coronavirus disease 2019 (COVID-19) seropositivity and asymptomatic rates in healthcare workers are associated with job function and masking. Clin Infect Dis. 2021;73:S154-S162. 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[PMID: 33853694] doi:10.1017/ice.2021.167 CrossrefMedlineGoogle Scholar Comments0 CommentsSign In to Submit A Comment Bruce B DuncanProfessor, School of Medicine, Federal University of Rio Grande do Sul29 March 2022 Natural experiments also support mask use / Comments to the evaluation of the Gonçalves et al. case-control study Findings in this systematic review are complemented by those of a review of natural experiments/ecologic studies: Ford N et al. Mask use in community settings in the context of COVID-19: A systematic review of ecological data. EclinicalMedicine 2021 Aug;38:101024. doi: 10.1016/j.eclinm.2021.101024. Epub 2021 Jul 19. Concerning the population-based case-control study by Goncalves et al 2021, as presented in Supplement Tables 2. (Study characteristics of new observational studies of mask use) and 4 (Quality assessment of new observational studies of mask), please note that: The words “Total cohort” are misleading, as the total cohort was the adult population of Porto Alegre, RS, Brazil excluding health professionals. Ascertainment of SARS-CoV-2 infection in controls was done by antibody testing. Although the participation rate was approximately 50%, the study did attempt to enroll all cases and a random sample of controls. The frequency of missing data was reported. Marknone2 April 2022 Actual findings from preeminent RCTs contrast conclusions for community setting Update 4 of this work upgraded to "low evidence" in favour of mass mask use (mandates) in community settings, based mostly on the DANMASK-19 trial results (1). However, the conclusion would have been the opposite according to the actual findings of that study, see (2) for a discussion. Again, upgraded in this last update - "low" to "low-moderate" - mostly from the Bangladesh clusters trial (3) seem unsupported according to re-analysis by Chikina, Pegden, Rech (4). REFERENCES 1. 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 wearer. A randomized controlled trial. Ann Intern Med 2020 Nov 18. doi: 10.7326/M20-6817 2. Abbasi K. The curious case of the Danish mask study BMJ 2020; 371 :m4586 doi:10.1136/bmj.m4586 3. Abaluck J, Kwong LH, Styczynski A, et al. Impact of community masking on COVID-19: A cluster-randomized trial in Bangladesh. Science. 2021 Dec 2; 375 (6577). doi: 1126/science.abi9069 4. Chikina M, Pegden W, Recht B. What were the effects of the Bangladesh mask intervention? [online] arg min blog. Available at: <https://www.argmin.net/2021/12/01/unblinding/> Roger ChouDepartment of Medical Informatics and Clinical Epidemiology, Oregon Health & Science University18 May 2022 Author Response to comment We thank readers for their interest and comments on our living review. “Mark” questions whether new evidence on masks in community settings warranted upgrading the strength of evidence. In Update Alert 7, we slightly strengthened the evidence for benefits of masks versus no masks in community settings to low-moderate, based on a large randomized trial conducted in Bangladesh (1) that found a mask intervention associated with 12% reduction in symptomatic SARS-CoV-2 seroprevalence. This finding was consistent with the results of a prior, Danish randomized trial (2). In the Bangladesh trial, differential recruitment occurred in intervention and control villages, with less participation in control villages. Differential recruitment could account for the observed benefit of the mask promotion intervention, if persons who declined to participate in the control group were less likely to become infected with SARS-CoV-2 than those who participated. However, nonparticipants in research studies usually experience worse outcomes than those who participate (3), which would tend to bias towards a null effect. Duncan cites a review by Ford and colleagues, which provides complementary information on masks from ecological studies (4). Ecological studies are not not eligible for our living systematic review (the lead author on this living review was also co-author on the Ford review). Regarding the Goncalves study, the term “total cohort” refers to the total cohort evaluated in the study (not the total population of Porto Alegre). Although ascertainment of SARS-CoV-2 infection in this study was adequate, the accuracy of methods used to ascertain exposures (interview questions) was unclear and potentially susceptible to recall bias. The study reported the number of patients in whom data on race were missing, but did not report missing data for other variables. References Abaluck J, Kwong LH, Styczynski A, et al. Impact of community masking on COVID-19: A cluster-randomized trial in Bangladesh. Science. 2021;375:eabi9069. doi:1126/science.abi9069. 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 wearer. A randomized controlled trial. Ann Intern Med. 2021;174:335-43. doi: 10.7326/M20-6817. Gerber Y, Jacobsen SJ, Killiam JM, Weston SA, Roger VL. Participation bias assessment in a community-based study of myocardial infarction, 2002-2005. Mayo Clin Proc. 2007;82:933-8. doi:10.4065/82.8.933. Ford N, Hollmer HK, Chou R, et al. Mask use in community settings in the context of COVID-19: A systematic review of ecological data. EClinicalMedicine. 2021;38:101024. doi: 10.1016/j.eclinm.2021.101024. Gonçalves MR, Dos Reis RCP, Tólio RP, et al. Social Distancing, Mask Use, and Transmission of Severe Acute Respiratory Syndrome Coronavirus 2, Brazil, April-June 2020. Emerg Infect Dis. 2021;27:2135-43. doi: 10.3201/eid2708.204757. Author, Article, and Disclosure InformationAffiliations: Disclaimer: The authors of this manuscript are responsible for its content. Statements in the manuscript do not necessarily represent the official views of or imply endorsement by the Agency for Healthcare Research and Quality or U.S. Department of Health and Human Services.Disclosures: Disclosures can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=L21-0783.Corresponding Author: Roger Chou, MD, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Mail Code BICC, Portland, OR 97239; e-mail, [email protected]edu.This article was published at Annals.org on 29 March 2022. PreviousarticleNextarticle Advertisement FiguresReferencesRelatedDetailsSee AlsoUpdate Alert: Masks for Prevention of Respiratory Virus Infections, Including SARS-CoV-2, in Health Care and Community Settings Roger Chou , Tracy Dana , Rebecca Jungbauer , Chandler Weeks , and Marian S. McDonagh Update Alert 2: Masks for Prevention of Respiratory Virus Infections, Including SARS-CoV-2, in Health Care and Community Settings Roger Chou , Tracy Dana , Rebecca Jungbauer , Chandler Weeks , and Marian S. McDonagh Masks for Prevention of Respiratory Virus Infections, Including SARS-CoV-2, in Health Care and Community Settings Roger Chou , Tracy Dana , Rebecca Jungbauer , Chandler Weeks , and Marian S. McDonagh Update Alert 3: Masks for Prevention of Respiratory Virus Infections, Including SARS-CoV-2, in Health Care and Community Settings Roger Chou , Tracy Dana , Rebecca Jungbauer , and Chandler Weeks Update Alert 4: Masks for Prevention of Respiratory Virus Infections, Including SARS-CoV-2, in Health Care and Community Settings Roger Chou , Tracy Dana , Rebecca Jungbauer , and Chandler Weeks Update Alert 5: Masks for Prevention of Respiratory Virus Infections, Including SARS-CoV-2, in Health Care and Community Settings Roger Chou , Tracy Dana , Rebecca Jungbauer , and Chandler Weeks Update Alert 6: Masks for Prevention of Respiratory Virus Infections, Including SARS-CoV-2, in Health Care and Community Settings Roger Chou , Tracy Dana , and Rebecca Jungbauer Update Alert 8: Masks for Prevention of Respiratory Virus Infections, Including SARS-CoV-2, in Health Care and Community Settings Roger Chou , Tracy Dana , and Rebecca Jungbauer Metrics Cited byMedical Masks Versus N95 Respirators for Preventing COVID-19 Among Health Care Workers A Randomized TrialMark Loeb, MD, Amy Bartholomew, MScN, Madiha Hashmi, MD, Wadea Tarhuni, MD, Mohamed Hassany, MD, Ilan Youngster, MD, Ranjani Somayaji, MD, Oscar Larios, MD, Joseph Kim, MD, Bayan Missaghi, MD, Joseph V. Vayalumkal, MD, Dominik Mertz, MD, Zain Chagla, MD, Maureen Cividino, MD, Karim Ali, MD, Sarah Mansour, MB BCh BAO, Lana A. Castellucci, MD, Charles Frenette, MD, Leighanne Parkes, MD, Mark Downing, MD, Matthew Muller, MD, PhD, Verne Glavin, MD, Jennifer Newton, BSc, Ravi Hookoom, BASc, Jerome A. Leis, MD, James Kinross, MD, Stephanie Smith, MD, Sayem Borhan, PhD, Pardeep Singh, BSc, Eleanor Pullenayegum, PhD, and John Conly, MD May 2022Volume 175, Issue 5Page: W58-W59 ePublished: 29 March 2022 Issue Published: May 2022 Copyright & PermissionsCopyright © 2022 by American College of Physicians. All Rights Reserved.PDF downloadLoading ...