Explaining vaccination decisions: A system dynamics model of the interaction between epidemiological and behavioural factors

The WHO goal of eradicating measles is delayed by widespread scepticism of parents against the recommended MMR vaccination. In this context, a model of the prevalence of measles that incorporates behavioural aspects is desirable. Parental decisions can be influenced by epidemiological and behavioural factors. The former include vaccination coverage and its impact on the prevalence of the disease. The latter include perceptions of the risk to be infected, which affects vaccination decisions, as well as government campaigns to affect vaccination behaviour, vaccination scares or changes in disease control policies. We develop a model that incorporates both kinds of effects. In particular, we illustrate how incorporating parental response to a change in the prevalence of the disease impacts the outcome of governmental policies aiming to increase the vaccination coverage. While calibrated to measles, this model is also applicable to other childhood diseases, such as pertussis or diphtheria. Different scenarios illustrate the long-term consequences of the interaction between health policies (in particular, vaccination campaigns) or the agenda of social institutions (e.g., drawing attention to specific events to create vaccination scares) and parental reactions. Periodic ups and downs of the disease's prevalence, characteristic of epidemiological feedback, are the consequence of the interaction between parental behaviour and events such as vaccination campaigns or vaccination scares. International and national health authorities, pursuing the fight against measles, may be helped by the potential of the model to provide understanding in the way different predictors of vaccination behaviour interact.