  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. By integrating the stochastic dynamics
of social activity into traditional epidemiological models we demonstrate the
emergence of a new long timescale governing the epidemic in broad agreement
with empirical data. Our model captures multiple features of real-life
epidemics such as COVID-19, including prolonged plateaus and multiple waves,
which are transiently suppressed due to the dynamic nature of social activity.
The existence of the long timescale due to the interplay between epidemic and
social dynamics provides a unifying picture of how a fast-paced epidemic
typically will transition to the endemic state.
