key: cord-0719286-uc37poce
authors: Javid, Babak; Balaban, Nathalie Q
title: Impact of population mask wearing on Covid-19 post lockdown
date: 2020-04-16
journal: nan
DOI: 10.1101/2020.04.13.20063529
sha: a3a3324af4dea9ef7d629e6af281e968e0495daf
doc_id: 719286
cord_uid: uc37poce

COVID-19, caused by SARS-CoV2 is a rapidly spreading global pandemic. Although precise transmission routes and dynamics are unknown, SARS-CoV2 is thought primarily to spread via contagious respiratory droplets. Unlike with SARS-CoV, maximal viral shedding occurs in the early phase of illness, and this is supported by models that suggest 40-80% of transmission events occur from pre- and asymptomatic individuals. One widely-discussed strategy to limit transmission of SARS-CoV2, particularly from presymptomatic individuals, has been population-level wearing of masks. Modelling for pandemic influenza suggests some benefit in reducing total numbers infected with even 50% mask-use. COVID-19 has a higher hospitalization and mortality rate than influenza, and the impacts on these parameters, and critically, at what point in the pandemic trajectory mask-use might exert maximal benefit are completely unknown. We derived a simplified SIR model to investigate the effects of near-universal mask-use on COVID-19 assuming 8 or 16% mask efficacy. We decided to model, in particular, the impact of masks on numbers of critically-ill patients and cumulative mortality, since these are parameters that are likely to have the most severe consequences in the COVID-19 pandemic. Whereas mask use had a relatively minor benefit on critical-care and mortality rates when transmissibility (Reff) was high, the reduction on deaths was dramatic as the effective R approached 1, as might be expected after aggressive social-distancing measures such as wide-spread lockdowns. One major concern with COVID-19 is its potential to overwhelm healthcare infrastructures, even in resource-rich settings, with one third of hospitalized patients requiring critical-care. We incorporated this into our model, increasing death rates for when critical-care resources have been exhausted. Our simple model shows that modest efficacy of masks could avert substantial mortality in this scenario. Importantly, the effects on mortality became hyper-sensitive to mask-wearing as the effective R approaches 1, i.e. near the tipping point of when the infection trajectory is expected to revert to exponential growth, as would be expected after effective lockdown. Our model suggests that mask-wearing might exert maximal benefit as nations plan their post-lockdown strategies and suggests that mask-wearing should be included in further more sophisticated models of the current pandemic.

COVID-19, caused by SARS-CoV2 is a rapidly spreading global pandemic. Although precise transmission routes and dynamics are unknown, SARS-CoV2 is thought primarily to spread via contagious respiratory droplets 1 . Unlike with SARS-CoV, maximal viral shedding occurs in the early phase of illness 1 , and this is supported by models that suggest 40-80% of transmission events occur from pre-and asymptomatic individuals 2,3 . One widely-discussed strategy to limit transmission of SARS-CoV2, particularly from presymptomatic individuals, has been population-level wearing of masks. Modelling for pandemic influenza suggests some benefit in reducing total numbers infected with even 50% mask-use 4 . COVID-19 has a higher hospitalization and mortality rate than influenza 5 , and the impacts on these parameters, and critically, at what point in the pandemic trajectory mask-use might exert maximal benefit are completely unknown.

We derived a simplified SIR model to investigate the effects of near-universal mask-use on COVID-19 assuming 8 or 16% mask efficacy (Supplementary information for relevant parameters and references). We decided to model, in particular, the impact of masks on numbers of critically-ill patients and cumulative mortality, since these are parameters that are likely to have the most severe consequences in the COVID-19 pandemic. Whereas mask use had a relatively minor benefit on critical-care and mortality rates when transmissibility (Reff) was high (Fig. 1a) , the reduction on deaths was dramatic as the effective R approached 1 (Fig. 1b) , as might be expected after aggressive socialdistancing measures such as wide-spread lockdowns 5 . One major concern with COVID-19 is its potential to overwhelm healthcare infrastructures, even in resource-rich settings, with one third of hospitalized patients requiring critical-care. We incorporated this into our model, increasing death rates for when critical-care resources have been exhausted (Fig. 1c ). Our simple model shows that modest efficacy of masks could avert substantial mortality in this scenario. Importantly, the effects on mortality became hyper-sensitive to mask-wearing as the effective R approaches 1, i.e. near the tipping point of when the infection trajectory is expected to revert to exponential growth, as would be expected after effective lockdown.

. CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint . https://doi.org/10.1101/2020. 04.13.20063529 doi: medRxiv preprint In order to understand the generality of the effect of mask wearing upon home confinement removal, we also analysed the potential effects of mask-wearing for data provided by a more comprehensive and realistic model of the COVID-19 infection, which included modelling of different levels of socialdistancing measures on infection and likely deaths 5 . When home-confinement is lifted but other social-distancing measures are in place, such as school closure and case isolation, wearing masks can maintain the benefits of home-confinement, both in terms of deaths (Fig. 1d) and critical-care bed use (Fig. 1e) .

Limitations of our study include the relatively straightforward model we employed, as well as assumptions of high compliance with mask-wearing and their potential efficacy, for which definitive evidence in pandemics is lacking 6 . Despite these limitations, our model suggests that mask-wearing might exert maximal benefit as nations plan their 'post-lockdown' strategies and suggests that maskwearing should be included in further more sophisticated models of the current pandemic. Since otherwise similar countries are currently devising different mask-wearing scenarios, the current situation offers an unprecedented opportunity to gather evidence on the real-world utility of population mask-wearing for implementation in this and future pandemics.

Word count: 524 words . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

(which was not peer-reviewed) The copyright holder for this preprint . https://doi.org/10.1101/2020.04.13.20063529 doi: medRxiv preprint

Virological assessment of hospitalized patients with COVID-2019

Quantifying SARS-CoV-2 transmission suggests epidemic control with digital contact tracing

Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV2)

Mathematical modeling of the effectiveness of facemasks in reducing the spread of novel influenza A (H1N1)

Nonpharmaceutical Measures for Pandemic Influenza in Nonhealthcare Settings-Personal Protective and Environmental Measures. Emerging infectious diseases

. CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.(which was not peer-reviewed) The copyright holder for this preprint . https://doi.org/10.1101/2020.04.13.20063529 doi: medRxiv preprint Table 4 ). Assuming a 10% reduction in infectivity, mask wearing may be at least as effective as home confinement at reducing deaths (D) or preventing overwhelming icu beds (E). The different bars (1) (2) (3) (4) (5) are different thresholds ("triggers") for implementing social measures in the Ferguson et al model.. CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.(which was not peer-reviewed) The copyright holder for this preprint . https://doi.org/10.1101/2020.04.13.20063529 doi: medRxiv preprint