Purpose <p>This systematic review and meta-analysis examined vaccine hesitancy and related vaccination behaviours in autism spectrum disorder (ASD)-related populations. We aimed to quantify the burden of hesitancy and synthesize evidence on refusal, delay, and under-vaccination among caregivers of children with ASD and, where available, autistic adults.</p> Methods <p>Following PRISMA 2020 and a prospectively registered PROSPERO protocol (CRD420251154536), we searched MEDLINE/PubMed, Web of Science, EBSCO, and TR Dizin from inception to 28 September 2025. Quantitative, qualitative, and mixed-methods studies addressing vaccine hesitancy or vaccination behaviours in ASD-related populations were eligible. Narrative synthesis was undertaken across all included studies, and meta-analysis was performed where outcomes were sufficiently comparable.</p> Results <p>Twenty studies were included (16 quantitative, 3 qualitative, 1 mixed-methods). Among studies using a common instrument and threshold (PACV ≥ 50), the pooled prevalence of vaccine hesitancy among caregivers of children with ASD was 23.65% (95% CI 15.87–33.71). Compared with caregivers of neurotypical children, caregivers of children with ASD had higher odds of vaccine hesitancy or refusal (pooled OR = 2.31, 95% CI 1.66–3.22). They also had higher odds than families of children with other neurodevelopmental conditions (pooled OR = 2.23, 95% CI 1.48–3.35). Sibling-focused analyses suggested greater under-vaccination among younger siblings in ASD-affected families (pooled RR = 3.20, 95% CI 2.59–3.96). Narrative findings consistently implicated the disproven MMR–autism claim, safety concerns, and distrust.</p> Conclusion <p>Vaccine hesitancy and related under-vaccination appear to be disproportionately concentrated in ASD-affected families. Autism-informed counselling, explicit myth-correction by trusted clinicians, and service adaptations may improve timely vaccine uptake.</p>