Vaccine hesitancy remains a major public-health issue, and behavioural science can help identify which features of an immunisation programme motivate acceptance and how subtle choice-architecture modifications might shift those motivations. We conducted two Bayesian D-optimal discrete-choice experiments that systematically varied eight clearly defined attributes of hypothetical vaccination programmes. Study 1 (N = 299) asked adults to choose for themselves or for their child, with the primary aim of (a) quantifying the importance of each attribute and (b) testing whether perspective alters that hierarchy. A doctor’s recommendation given during a visit emerged as the dominant driver of choice, followed by side-effect severity and acquaintances’ opinion; the self-versus-child perspective did not affect the importance given to each of those factors. Study 2 (N = 327) introduced a factorial manipulation of two behavioural interventions—a descriptive social-norm nudge (“most participants chose this option”) and a competence-boost (heuristic endorsement by a reputable research institute)—while retaining the two decision perspectives. The study’s aims were to evaluate (c) whether either intervention directly increases vaccine uptake and (d) how interventions interact with the existing attribute structure. Both interventions raised the overall likelihood of choosing to get vaccinated, yet their effects were highly context-specific: they strengthened the influence of some cues (e.g., many sick acquaintances) while attenuating or reversing others (notably high efficacy and positive mandates). These results show that social-norm nudges and heuristic boosts can promote vaccination, but only when aligned with the prevailing attribute landscape and supported by credible clinical recommendations.