Aim <p>The effectiveness of vaccines in preventing infectious disease and counteracting its negative consequences is now an established assumption in the literature. However, vaccine hesitancy remains one of the most significant worldwide public health concerns; accordingly, the investigation of determinants stimulating or contrasting the phenomenon has a crucial role. In this context, on the basis of literature findings, it can be assumed that one of the significant factors inhibiting vaccine action is vaccine unawareness. Therefore, the present study aimed to develop and validate a new instrument for measuring it: the Vaccine Unawareness Scale (VUS).</p> Subject and methods <p>Data were anonymously and voluntarily collected through an online survey; the final sample comprised 636 individuals (78.2% cis-gender females; mean age = 27 years, SD = 10).</p> Results <p>Both confirmatory factor analysis (CFA) and correlation analysis were performed to validate the VUS internally and externally. The CFA supported a one-factor model composed of four items, showing an optimal fit for the VUS. The instrument was also characterized by acceptable internal reliability (Cronbach’s α = 0.789). Furthermore, results showed significant correlations between the VUS and several dimensions concerning risk perception, anxiety and fear about vaccination, and vaccine hesitancy. The observed correlations had the expected directionality, with effect sizes ranging from relatively small to typical values.</p> Conclusion <p>Given the results achieved, the VUS appears to be a suitable and valuable instrument for measuring vaccine unawareness by enriching literature findings concerning the determinants positively and negatively linked to vaccination.</p>