  We study how homophily of human physical interactions affects the efficacy of
digital proximity tracing. Analytical results show a non monotonous dependence
of the reproduction number with respect to the mixing rate between individuals
that adopt the contact tracing app and the ones that do not. Furthermore, we
find regimes in which the attack rate has local optima, minima or monotonously
varies with the mixing rate. We corroborate our findings with Monte Carlo
simulations on a primary-school network. This study provides a mathematical
basis to better understand how homophily in health behavior shapes the dynamics
of epidemics.
