In this paper, we study the dynamics of contagious spreading processes taking place in complex contact networks. We specifically present a lower-bound on the decay rate of the number of nodes infected by a susceptible-infectedsusceptible (SIS) stochastic spreading process. A precise quantification of this decay rate is crucial for designing efficient strategies to contain epidemic outbreaks. However, existing lower-bounds on the decay rate based on first-order mean-field approximations are often accompanied by a large error resulting in inefficient containment strategies. To overcome this deficiency, we derive a lower-bound based on a second-order moment-closure of the stochastic SIS processes. The proposed second-order bound is theoretically guaranteed to be tighter than existing first-order bounds. We also present various numerical simulations to illustrate how our lower-bound drastically improves the performance of existing first-order lower-bounds in practical scenarios, resulting in more efficient strategies for epidemic containment.Understanding the dynamics of spreading processes taking place in complex networks is one of the central questions in the field of network science, with applications in information propagation in social networks [1], epidemiology [2], and cyber-security [3]. Among various quantities characterizing the asymptotic behaviors of spreading processes, the decay rate (see, e.g., [4,5]) of the spreading size (i.e., the number of nodes affected by the spread) is of fundamental importance. Besides quantifying the impact of contagious spreading processes over networks [6,7], the decay rate has been used to measure the performance of containment strategies to control epidemic outbreaks [8]. In this direction, the authors in [9] presented an optimization-based approach for distributing a limited amount of resources to efficiently contain spreading processes by maximizing their decay rate towards the disease-free equilibrium. This framework was later extended to the cases where the underlying network in which the spreading process is taking place is uncertain [10], temporal [11,12], and adaptively changing [13,14]. Recently, the authors in [15] presented an approach for achieving an optimal resource allocation in order to maximize the decay rate under sparsity constraints.However, finding the decay rate of a spreading process is, in general, a computationally hard problem. Even for the case of the susceptible-infectedsusceptible (SIS) model [2], which is one of the simplest models of spread, the exact decay rate is given in terms of the eigenvalues of a matrix whose size grows exponentially fast with respect to the number of nodes in the networks [4]. In order to avoid this computational difficulty, it is common in the literature [9,10,15] to use a lower-bound on the decay rate based on first-order mean-field approximations of the spreading processes. However, this first-order approximation is not necessarily accurate; in other words, its approximation error can be significantly large for seve...