CAN’T STAND WITH THESE MEASURES Uncovering the psychophysiological roots of vaccine intentions and attitudes

This compendium of studies presents an exploratory investigation into an integrated range of psychological, psychophysiological, and psychosocial factors associated with Vaccine Hesitancy (VH). By adopting diverse methodological and theoretical lenses, this research endeavors to construct a novel, multi-dimensional framework to investigate the underlying processes that drive resistance to vaccination efforts. The primary goal of this thesis is to provide preliminary experimental evidence that can inform public health communication strategies. VH is framed as a complex phenomenon influenced by physiological, cognitive, affective, and moral layers that must be understood holistically. The first study investigates the potential alignment between psychophysiological reactivity and the affective dimensions of Vaccine Hesitancy (VH). Using Motor Evoked Potentials (MEPs), we measured corticospinal excitability during the observation of vaccination-related images. Results revealed a robust, muscle-specific main effect: injection scenes elicited higher MEP amplitudes in the deltoid compared to control muscles, suggesting a foundational motoric readiness to a perceived threat to bodily integrity. Notably, this physiological response appeared invariant across vaccine types and did not show a significant interaction with individual VH levels. In contrast, a significant effect emerged in subjective affective ratings, where higher VH scores were associated with heightened disgust and anger toward vaccination imagery. These preliminary findings suggest a dissociation between automatic somatic defense and subjective emotional "filtering": while the motor system reacts to the physical act of penetration, VH selectively modulates the affective appraisal of the vaccine as a potential source of violation. Building on the link between affect and morality, the second study investigates moral reasoning by conceptualizing vaccination as a social dilemma (utilitarian vs. deontological conflict). Utilizing a set of incidental moral dilemmas, we explored whether individual vulnerability to misinformation moderates the relationship between general moral strategies and VH. The results suggest that individuals may adopt distinct reasoning styles depending on their misinformation levels; specifically, more informed hesitant individuals appear to exhibit a deontological rigidity that mirrors their vaccine stance. These results are discussed with due caution, highlighting how moral decision-making processes may serve as exploratory predictors of vaccine attitudes. The third study extends the investigation into the social-cognitive domain, exploring whether the affective reactions and moral rigidity identified in the previous experiments manifest as implicit social bias. Grounded in the "behavioral immune system" framework, we examined whether the heightened disgust and anger elicited by vaccination (Study 1) were associated with implicit prejudice toward outgroups traditionally linked to purity or safety threats (black and homosexual individuals). Using the Implicit Association Test (IAT), we explored these associations in a young, post-pandemic Italian cohort. Despite the theoretical premise that affective cues of "violation" might drive social derogation, the results were null, showing no significant link between implicit bias and VH. These findings are discussed in light of the exploratory nature of the work, suggesting that while the "body" may react with disgust to the medical act, this does not necessarily translate into stable, automatic social prejudice in lowthreat environments. In summary, this thesis offers a preliminary perspective on VH, tentatively exploring its psychophysiological, moral, and social-cognitive underpinnings. The findings suggest that VH may involve a selective emotional filtering—manifesting as anger or disgust—that appears to be dissociated from automatic, muscle-specific motor defenses. Furthermore, hesitancy seems intertwined with deontological moral reasoning, which may be further complicated by misinformation and low institutional trust. While the null results in specific VH-related motor-physiological reactivity and social bias provide tentative boundary conditions, they suggest that the visceral and social correlates of VH are highly context-dependent. We propose that future communication might benefit from moving beyond "correcting information" to cautiously address these deeper, embodied, and moral appraisals that characterize the hesitant experience.