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Scale-free dynamics of Covid-19 in a Brazilian city

By Josue M. P. Policarpo, Arthur A. G. F. Ramos, Christopher Dye, Nuno R. Faria, Fabio E. Leal, Osmar J S Moraes, Kris V Parag, Pedro S Peixoto, Ester C. Sabino, Vitor H. Nascimento, Airton Deppman

Posted 15 Sep 2021
medRxiv DOI: 10.1101/2021.09.10.21263332

Mathematical models can provide insights into the control of pandemic COVID-19, which remains a global priority. The dynamics of directly-transmitted infectious diseases, such as COVID-19, are usually described by compartmental models where individuals are classified as susceptible, infected and removed. These SIR models typically assume homogenous transmission of infection, even in large populations, a simplification that is convenient but inconsistent with observations. Here we use original data on the dynamics of COVID-19 spread in a Brazilian city to investigate the structure of the transmission network. We find that transmission can be described by a network in which each infectious individual has a small number of susceptible contacts, of the order of 2-5, which is independent of total population size. Compared with standard models of homogenous mixing, this scale-free, fractal infection process gives a better description of COVID-19 dynamics through time. In addition, the contact process explains the geographically localized clusters of disease seen in this Brazilian city. Our scale-free model can help refine criteria for physical and social

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