Homophily impacts the success of vaccine roll-outs

TL;DR

This paper investigates how homophily influences vaccine distribution effectiveness, revealing complex dynamics and regimes that affect disease control, supported by simulations on contact networks.

Contribution

It uncovers three distinct dynamical regimes of vaccine impact based on mixing rates, a novel insight into homophily's role in epidemic spread.

Findings

Attack rate decreases, increases, or varies non-monotonically with mixing rate.

Homophily creates different epidemic regimes depending on parameters.

Results are supported by Monte Carlo simulations on contact networks.

Abstract

Physical contacts do not occur randomly, rather, individuals with similar socio-demographic and behavioural characteristics are more likely to interact among them, a phenomenon known as homophily. Concurrently, the same characteristics correlate with the adoption of prophylactic tools. As a result, the latter do not unfold homogeneously in a population, affecting their ability to control the spread of infectious diseases. Here, focusing on the case of vaccines, we reveal three different dynamical regimes as a function of the mixing rate between vaccinated and non vaccinated individuals. Specifically, depending on the epidemic pressure, vaccine coverage and efficacy, we find the attack rate to decrease, increase or vary non monotonously with respect to the mixing rate. We corroborate the phenomenology through Monte Carlo simulations on a temporal physical contact network. Besides vaccines, our findings hold for a wide range of prophylactic tools, indicating a universal mechanism in spreading dynamics