key: cord-0865958-r1a2zwj4 authors: Chowell, Diego; Chowell, Gerardo; Roosa, Kimberlyn; Dhillon, Ranu; Srikrishna, Devabhaktuni title: Sustainable social distancing through facemask use and testing during the Covid-19 pandemic date: 2020-04-06 journal: nan DOI: 10.1101/2020.04.01.20049981 sha: 4eb1a40e3c30cbd54d5349d4e25db1ad25f2b39b doc_id: 865958 cord_uid: r1a2zwj4 We investigate how individual protective behaviors, different levels of testing, and isolation influence the transmission and control of the COVID-19 pandemic. Based on an SEIR-type model incorporating asymptomatic but infectious individuals (40%), we show that the pandemic may be readily controllable through a combination of testing, treatment if necessary, and self-isolation after testing positive (TTI) of symptomatic individuals together with social protection (e.g., facemask use, handwashing). When the basic reproduction number, R0, is 2.4, 65% effective social protection alone (35% of the unprotected transmission) brings the R below 1. Alternatively, 20% effective social protection brings the reproduction number below 1.0 so long as 75% of the symptomatic population is covered by TTI within 12 hours of symptom onset. Even with 20% effective social protection, TTI of 1 in 4 symptomatic individuals can substantially 'flatten the curve' cutting the peak daily incidence in half. (A) Total number of infections in a population of 10 million individuals for varying levels of social protection and testing (TTI) at 12 hours testing delay and assuming 40% asymptomatic transmission. (B) Daily incidence in a population of 10 million individuals for 20% effectiveness of social protection and varying levels of testing (TTI) at 12 hours testing delay and assuming 40% asymptomatic transmission. Initial conditions were set as follows, susceptible individuals: 9,943,400; symptomatic individuals who underwent testing: 40,000; asymptomatic individuals: 16,000; and deceased individuals: 600. Basic reproduction number, R0 The basic reproduction number, R0, is defined as the average number of secondary cases generated by primary infectious individuals during the early transmission phase in a completely susceptible population and in the absence of control interventions. This is a key metric to gauge the intensity and type of interventions that need to be implemented in order to bring the epidemic under control. For the ongoing epidemic of 2019-nCov, R0 has been estimated at 2.4 (3.9, upper bound of 95% confidence interval). The reproductive number, R, quantifies the potential for infectious disease transmission in the context of a partially susceptible population. When R > 1, infection may spread in the population, and the rate of spread is higher with increasingly high values of R. If R < 1, infection cannot be sustained and is unable to generate an epidemic. As there are seven classes contributing to new infections, the reproduction number is the sum of the contributions of the infectious classes: The contributions of the individual compartments are as follows & All rights reserved. No reuse allowed without permission. author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/2020.04.01.20049981 doi: medRxiv preprint Compartmental transmission models are commonly used in infectious disease epidemiology as a population-level modeling approach that subdivides the population into various classes based on epidemiological status. Compartmental models are specified by a set parameters and ordinary differential equations that track the progression of the number of individuals within each state. Here, we developed an extension of the commonly used SEIR transmission model for modeling the transmission of COVID-19. Individuals within the model are classified as susceptible (S), latent (E1), partially infectious but not yet symptomatic (E2), asymptomatic and will not be tested (An), asymptomatic and will be tested and will be isolated (As), infectious and will not be tested (In), infectious and will be tested Individuals in E1 progress to E2 at rate κ1. Individuals from E2 are partially infectious, with relative transmissibility qe, and progress at rate κ2, where a proportion ρa become asymptomatic and partially infectious (relative transmissibility qa), and 1 -ρa become fully infectious. Among the proportion ρa who become asymptomatic, ns will be tested, while 1-ns will be undetected. Further, among the proportion 1 -ρa that become fully infectious, ρs will be tested, while 1 -ρs will be undetected. Asymptomatic individuals who are not tested and symptomatic individuals wear personal protective equipment (PPE) (such as wearing masks in public, handwashing, etc) and thus have relative transmissibility q, which is proportional to the level of effectives of PPE. Individuals within An and In classes (who are not tested) recover at rate γ1. Those who are tested All rights reserved. No reuse allowed without permission. author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/2020.04.01.20049981 doi: medRxiv preprint (Is and As) will progress to the hospitalized and isolated class at diagnosis rate α, where relative transmission within hospitals and isolated places, h, can occur. However, we assume perfection isolation in our analyses. Individuals who are hospitalized and isolated progress to the recovered class at rate γ2 or to the deceased class at rate δ. Therefore, the system is defined by the following system of non-linear differential equations: Relative transmissibility of exposed individuals 0.1 [1] qa Relative transmissibility of asymptomatic cases 0.4 [1] All rights reserved. No reuse allowed without permission. author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint (which was not peer-reviewed) is the Length of infectiousness prior to symptom onset 2.5 days [4] [5] [6] [7] ρa Proportion of exposed individuals who become asymptomatically infected 20%, 40%, and 60% [8, 9] ns Proportion of asymptomatic individuals who will be tested and isolated δ Death rate within hospitals = 0.04 [11] All rights reserved. No reuse allowed without permission. author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/2020.04.01.20049981 doi: medRxiv preprint Figure 1 . Thresholds for social protection and testing / isolation needed to bring R < 1. author/funder, who has granted medRxiv a license to display the preprint in perpetuity. author/funder, who has granted medRxiv a license to display the preprint in perpetuity. 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