  Epidemic models study the spread of an undesired agent through a population,
be it infectious diseases through a country, misinformation in online social
media, or pests infesting a region. In combating these epidemics, we rely
neither on global top-down interventions, nor solely on individual adaptations.
Instead, interventions most commonly come from local institutions such as
public health departments, moderation teams on social media platforms, or other
forms of group governance. Classic models, which are often individual or
agent-based, are ill-suited to capture local adaptations. We leverage recent
development of institutional dynamics based on cultural group selection to
study how groups can attempt local control of an epidemic by taking inspiration
from the successes and failures of other groups. Incorporating these
institutional changes into the epidemic dynamics reveals paradoxes: a higher
transmission rate can result in smaller outbreaks and decreasing the speed of
institutional adaptation generally reduces outbreak size. When groups perceive
a contagion as more worrisome, they can invest in improved policies and, if
they maintain these policies long enough to have impact, lead to a reduction in
endemicity. By looking at the interplay between the speed of institutions and
the transmission rate of the contagions, we find rich co-evolutionary dynamics
that reflect the complexity of known biological and social contagions.
