Traffic-driven sequential spread of two interacting epidemics on complex networks

While the coupling between traffic dynamics and epidemic spreading on complex networks has been widely studied, existing research has predominantly focused on single-pathogen transmission. In this paper, we investigate the sequential spreading dynamics of two interacting epidemics driven by traffic flow. The model incorporates a key mechanism whereby prior infection with the first disease alters a node’s susceptibility to the second disease. We develop a heterogeneous mean-field framework for the coupled spreading process and derive analytical expressions for the epidemic thresholds. Our results show that the interaction parameter α and the infection rate of the first epidemic β ₁ jointly determine the outbreak threshold and stationary prevalence of the second epidemic. The parameter α regulates how prior infection influences susceptibility to the second epidemic, ranging from suppressive interaction (α < 1) through neutral interaction (α = 1) to synergistic interaction (α > 1). A pronounced nonlinear threshold response emerges: in the suppressive interaction regime, increasing β ₁ below its critical point substantially raises the epidemic threshold of the second disease, whereas in the synergistic interaction regime, it lowers the threshold. Once the first epidemic exceeds its critical point, both effects gradually saturate. Numerical simulations show good agreement with the theoretical predictions and further demonstrate the robustness of the results across different network sizes and average degrees. These findings reveal how epidemic interactions and network structure jointly shape sequential spreading dynamics in traffic-driven systems, providing new insights into coupled contagion processes on complex networks.