Vaccination and public trust: A model for the dissemination of vaccination behaviour with external intervention

Vaccination is widely recognized as the most effective way of immunization against many infectious diseases. However, unfounded claims about supposed side effects of some vaccines have contributed to spread concern and fear among people, thus inducing vaccination refusal. MMR (Measles, Mumps and Rubella) vaccine coverage has undergone an important decrease in a large part of Europe and US as a consequence of erroneously alleged side effects, leading to recent measles outbreaks. There is evidence that clusterization of unvaccinated individuals may lead to epidemics way larger that the ones that might appear in the case that unvaccinated agents are distributed at random in the population. In this work we explore the emergence of those clusters as a consequence of the social interaction driven mainly by homophily, where vaccination behaviour is part of a process of cultural dissemination in the spirit of Axelrod's model. The ingredients of this calculation encompass: (i) interacting agents which are to decide if they vaccinate or not their children, (ii) their interaction with a small subset of stubborn agents who believe that the MMR vaccine is not safe and (iii) government sponsored propaganda trying to convince people of the benefits of vaccination. We find that these clusters, which emerge as a dynamical outcome of the model, are the responsible of the increasing probability of the occurrence of measles outbreaks, even in scenarios where the WHO (World Health Organization) recommendation of 95% vaccine coverage is fulfilled. However, we also illustrate that the mitigating effect of a public health campaign, could effectively reduce the impact and size of outbreaks.