Mass mask-wearing notably reduces COVID-19 transmission

Abstract

Mask-wearing has been a controversial measure to control the COVID-19 pandemic. While masks are known to substantially reduce disease transmission in healthcare settings (Howard et al 2021), studies in community settings report inconsistent results (Brainard et al 2020). Investigating the inconsistency within epidemiological studies, we find that a commonly used proxy, government mask mandates, does not correlate with large increases in mask-wearing in our window of analysis. We thus analyse the effect of mask-wearing on transmission instead, drawing on several datasets covering 92 regions on 6 continents, including the largest survey of individual-level wearing behaviour (n=20 million) (Kreuter et al 2020). Using a hierarchical Bayesian model, we estimate the effect of both mask-wearing and mask-mandates on transmission by linking wearing levels (or mandates) to reported cases in each region, adjusting for mobility and non-pharmaceutical interventions. We assess the robustness of our results in 123 experiments across 22 sensitivity analyses. Across these analyses, we find that an entire population wearing masks in public leads to a median reduction in the reproduction number R of 25.8%, with 95% of the medians between 22.2% and 30.9%. In our window of analysis, the median reduction in $R$ associated with the wearing level observed in each region was 20.4% [2.0%, 23.3%]. We do not find evidence that mandating mask-wearing reduces transmission. Our results suggest that mask-wearing is strongly affected by factors other than mandates. We establish the effectiveness of mass mask-wearing, and highlight that wearing data, not mandate data, are necessary to infer this effect.

Behaviour, booster vaccines and waning immunity: modelling the medium-term dynamics of SARS-CoV-2 transmission in England in the Omicron era

“…Since late August 2021, mask wearing in England has decreased by approximately 30% 33 . We assume that this decrease could be completely reversed by the face covering measure, and that this would result in a 7.5% reduction in R over the contingency period, comparable to the effect size measured in a regression analysis across 92 regions 34 and a cluster randomized trial in Bangladesh 35 .…”

Global monitoring of the impact of the COVID-19 pandemic through online surveys sampled from the Facebook user base

“…With each survey version, new questions have been added in conjunction with epidemiologists, local government input, and research partners. Other studies have used these data to investigate a range of insights, including masking effectiveness, testing practices, and vaccine hesitancy, and there is potential to further understand knowledge, attitudes, and practices through this high-density data stream (30,(47)(48)(49)(50). Indeed, the survey has most recently incorporated items to survey social impacts, vaccine uptake, and vaccine hesitancy (31).…”

Unmasking the truth: experimental evidence of facemask compliance in Bangladesh, Kenya, and Nigeria during the COVID-19 pandemic

“…3 Non-randomized studies have also generally found that high levels of compliance are needed to reduce transmission at the community level. [28][29][30] Thus, effectiveness facemask mandates to reduce population-level transmission of COVID-19 requires both high levels of mask-wearing -and importantly the ability accurately measure actual compliance. Commonly used self-reported surveys are likely overestimating facemask compliance.…”