Validation of an Italian tool to assess vaccine literacy in adulthood vaccination: a pilot study

Vaccine Literacy (VL) is based on the same idea of Health Literacy (HL): it involves people's knowledge, motivation and competence to find, understand and use information to take decisions about children's and adults' vaccination. Using general measures, the association between HL and Vaccine Hesitancy has been shown to be inconsistent. HLVa-IT is a new tool, specific for the self-assessment of three VL scales, functional, interactive and critical about adults' immunization. Following a face validation process, HLVa-IT has been used to assess VL levels in a population of 50-75 years of age at the Public Health Unit of Latina (Latium, Italy). In order to validate its theoretical construct, it was administered at the same time with a Vaccine Quiz (VQ), assuming that subjects showing good knowledge about vaccination should have adequate VL. The consistent positive correlation for all three VL scales with the VQ score (Spearman's r=0.320, P=0.0004; r=0.389. P=0.0001 and r=0.306, P=0.0022, respectively), as well as with the educational degree, confirm the valid construct of HLVa-IT. A criterion validity of this tool has also been sought verifying its relation with acceptance of vaccines (VA) recommended in the adult/senior age. A positive association with VA observed only on the functional scale in the population ≥ 65 years, does not permit to accept a predictive validity, confirming that direct effect of Health Literacy is more clearly verifiable on knowledge than behavior outcomes. Nevertheless, HLVa-IT has shown suitable psychometric characteristics for the subjective measure of VL in individuals and in population studies. It is desirable that more specific tools are validated and extensively used, with the aim of assessing peoples' VL skills and defining interventions aimed at their improvement.