How Implicit Attitudes toward Vaccination Affect Vaccine Hesitancy and Behaviour: Developing and Validating the V-IRAP.

Vaccination is one of the most important ways of fighting infectious diseases, such as COVID-19. However, vaccine hesitancy and refusal can reduce adherence to vaccination campaigns, and therefore undermine their effectiveness. Although the scientific community has made great efforts to understand the psychological causes of vaccine hesitancy, studies on vaccine intention have usually relied on traditional detection techniques, such as questionnaires. Probing these constructs explicitly could be problematic due to defense mechanisms or social desirability. Thus, a measure capable of detecting implicit attitudes towards vaccination is needed. To achieve this aim, we designed and validated a new test called the Vaccine-IRAP, or V-IRAP, which is a modified version of the original Implicit Relational Assessment Procedure, or IRAP, task. The V-IRAP allows the unspoken reasons behind vaccine hesitancy to be investigated, and is able to distinguish between positive and negative beliefs on vaccination. The test was assessed in a sample of 151 participants. The V-IRAP showed good internal reliability and convergent validity, with meaningful correlational patterns with explicit measures. Moreover, it revealed incremental validity over such explicit measures. Lastly, the V-IRAP was able to shed light on the implicit attitudes involved in vaccine refusal, revealing negative attitudes relative to vaccine-related risks in non-vaccinated participants. Overall, these results support V-IRAP as a sensitive and reliable tool that could be used in future studies on implicit attitudes toward vaccination.