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The introduction of a mandatory mask policy was associated with significantly reduced COVID-19 cases in a major metropolitan city.
Scott, Nick; Saul, Allan; Spelman, Tim; Stoove, Mark; Pedrana, Alisa; Saeri, Alexander; Grundy, Emily; Smith, Liam; Toole, Michael; McIntyre, Chandini Raina; Crabb, Brendan S; Hellard, Margaret.
  • Scott N; The Burnet Institute, Melbourne, Australia.
  • Saul A; Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia.
  • Spelman T; The Burnet Institute, Melbourne, Australia.
  • Stoove M; The Burnet Institute, Melbourne, Australia.
  • Pedrana A; The Burnet Institute, Melbourne, Australia.
  • Saeri A; Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia.
  • Grundy E; The Burnet Institute, Melbourne, Australia.
  • Smith L; Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia.
  • Toole M; BehaviourWorks Australia, Monash Sustainable Development Institute, Monash University, Melbourne, Australia.
  • McIntyre CR; BehaviourWorks Australia, Monash Sustainable Development Institute, Monash University, Melbourne, Australia.
  • Crabb BS; BehaviourWorks Australia, Monash Sustainable Development Institute, Monash University, Melbourne, Australia.
  • Hellard M; The Burnet Institute, Melbourne, Australia.
PLoS One ; 16(7): e0253510, 2021.
Article in English | MEDLINE | ID: covidwho-1319515
ABSTRACT

BACKGROUND:

Whilst evidence of use of face masks in reducing COVID-19 cases is increasing, the impact of mandatory use across a large population has been difficult to assess. Introduction of mandatory mask use on July 22, 2020 during a resurgence of COVID-19 in Melbourne, Australia created a situation that facilitated an assessment of the impact of the policy on the epidemic growth rate as its introduction occurred in the absence of other changes to restrictions. METHODS AND

FINDINGS:

Exponential epidemic growth or decay rates in daily COVID-19 diagnoses were estimated using a non-weighted linear regression of the natural logarithm of the daily cases against time, using a linear spline model with one knot (lspline package in R v 3.6.3). The model's two linear segments pivot around the hinge day, on which the mask policy began to take effect, 8 days following the introduction of the policy. We used two forms of data to assess change in mask usage images of people wearing masks in public places obtained from a major media outlet and population-based survey data. Potential confounding factors (including daily COVID-19 tests, number of COVID-19 cases among population subsets affected differentially by the mask policy-e.g., healthcare workers) were examined for their impact on the results. Daily cases fitted an exponential growth in the first log-linear segment (k = +0.042, s.e. = 0.007), and fitted an exponential decay in the second (k = -0.023, s.e. = 0.017) log-linear segment. Over a range of reported serial intervals for SARS-CoV-2 infection, these growth rates correspond to a 22-33% reduction in an effective reproduction ratio before and after mandatory mask use. Analysis of images of people in public spaces showed mask usage rose from approximately 43% to 97%. Analysis of survey data found that on the third day before policy introduction, 44% of participants reported "often" or "always" wearing a mask; on the fourth day after, 100% reported "always" doing so. No potentially confounding factors were associated with the observed change in growth rates.

CONCLUSIONS:

The mandatory mask use policy substantially increased public use of masks and was associated with a significant decline in new COVID-19 cases after introduction of the policy. This study strongly supports the use of masks for controlling epidemics in the broader community.
Subject(s)

Full text: Available Collection: International databases Database: MEDLINE Main subject: Policy / COVID-19 / Masks Type of study: Experimental Studies / Observational study Limits: Humans Country/Region as subject: Oceania Language: English Journal: PLoS One Journal subject: Science / Medicine Year: 2021 Document Type: Article Affiliation country: Journal.pone.0253510

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Full text: Available Collection: International databases Database: MEDLINE Main subject: Policy / COVID-19 / Masks Type of study: Experimental Studies / Observational study Limits: Humans Country/Region as subject: Oceania Language: English Journal: PLoS One Journal subject: Science / Medicine Year: 2021 Document Type: Article Affiliation country: Journal.pone.0253510