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. 2020 Jun 25;139:110030. doi: 10.1016/j.chaos.2020.110030

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Since January 2020 Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on the novel coronavirus COVID-19. The COVID-19 resource centre is hosted on Elsevier Connect, the company's public news and information website. Elsevier hereby grants permission to make all its COVID-19-related research that is available on the COVID-19 resource centre - including this research content - immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for free by Elsevier for as long as the COVID-19 resource centre remains active.

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Fig. 14 — Existence for the COVID-19 system (10), of two stable equilibrium points: The DFE E₀, a stable endemic equilibrium $E_{2} = (1938.62, 657.11, 34941.36, 36511.93),$ and an unstable endemic equilibrium $E_{1} = (13687.91, 412.38, 61442.11, 8992.32)$ when $β_{r} = 0.07, σ = 0.155 (R_{c} = 0.50167) .$