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On the expected total number of infections for virus spread on a finite network. (English) Zbl 1322.60206
Summary: In this work we consider a simple SIR infection spread model on a finite population of $$n$$ agents represented by a finite graph $$G$$. Starting with a fixed set of initial infected vertices the infection spreads in discrete time steps, where each infected vertex tries to infect its neighbors with a fixed probability $$\beta\in(0,1)$$, independently of others. It is assumed that each infected vertex dies out after a unit time and the process continues till all infected vertices die out. This model was first studied by M. Draief et al. [Ann. Appl. Probab. 18, No. 2, 359–378 (2008; Zbl 1137.60051)]. In this work, we find a simple lower bound on the expected number of ever infected vertices using a breath-first search algorithm and show that it asymptotically performs better for a fairly large class of graphs than the upper bounds obtained in [loc. cit.]. As a by product, we also derive the asymptotic value of the expected number of the ever infected vertices when the underlying graph is the random $$r$$-regular graph and $$\beta<\frac{1}{r-1}$$.
##### MSC:
 60K35 Interacting random processes; statistical mechanics type models; percolation theory 60J80 Branching processes (Galton-Watson, birth-and-death, etc.) 60J85 Applications of branching processes 05C80 Random graphs (graph-theoretic aspects) 92D30 Epidemiology
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