How dynamic social activity shapes an epidemic: waves, plateaus, and endemic state

It is well recognized that population heterogeneity plays an important role in the spread of epidemics. While individual variations in social activity are often assumed to be persistent, i.e. constant in time, here we discuss the consequences of dynamic heterogeneity. We integrate the stochastic dynamics of social activity into traditional epidemiological models. The overall epidemic dynamics is condensed to three differential equations and is characterized by an emergent long timescale. Our model captures multiple features of real-life epidemics such as COVID-19, including prolonged plateaus and multiple waves. Individual waves are suppressed at the state of Transient Collective Immunity (TCI), which subsequently degrades due to the dynamic nature of social activity. Our results also provide a new mechanism for emerging pathogens to transition from a fast-paced epidemic to the endemic state.