Behavioural determinants of parents’ vaccination decisions

Childhood immunisation effectively protects personal and public health, but a sizeable minority of parents actively reject vaccines for their children. This Thesis explores how parents decide whether to have their children immunised, in order to inform efforts to improve immunisation uptake. A consistent profile of beliefs relating to vaccine rejection emerged across a systematic review of existing evidence, a semi-structured interview study (n=24), and two evidence-based questionnaire studies (n=900), which all focused on the measles, mumps and rubella (MMR) vaccine. Vaccine-rejecting parents doubted vaccine safety and efficacy, mistrusted health professionals and immunisation policy, perceived ‘pro-vaccine’ bias in most available information, believed most vaccine-preventable diseases are mild and uncommon, and were not motivated by the potential social benefits of MMR uptake. The review also indicated several pervasive methodological flaws in the evidence – including retrospective designs, parent-reported outcomes, and lack of multifactorial models – which were remedied in the new empirical work. Three behavioural experiments (n=703) were then used to explore the influence of this belief profile on immunisation decision-making under controlled conditions. These experiments indicated that the belief profile was less influential when decision-makers mistrusted vaccine providers and policy, were generally anxious, or sought to assimilate multiple belief profile factors on the basis of limited information. They also showed that information processing limitations and biases may influence decisions independently of information content, and accordingly written risk communication method was found in the final study (n=42) to impact on outcomes even after adjusting for information content. These findings indicate that parents’ immunisation decisions are typically not borne of simple vaccine versus disease risk-benefit analyses. Interventions to increase trust in the immunisation system and to communicate the social desirability (and normality) of vaccine acceptance may improve immunisation uptake and support informed, satisfying decision-making