Reframing Adolescent Under-Vaccination as a Delivery-System Transition Problem: A Response to Deck et al

This letter responds to Deck et al. (2026) and argues that their findings are better understood as evidence of health system performance at transition points than of adolescent vaccine hesitancy alone. Three patterns support this interpretation: the contrast between uniformly low influenza uptake and higher HPV coverage in younger cohorts, the sharp decline in coverage among older youth after school-based eligibility, and the poorer uptake among recent immigrants who may not be captured by established delivery pathways. Together, these findings suggest that under-vaccination accumulates when adolescents age out of school-based programmes, miss catch-up opportunities, or enter the system through newcomer pathways that are poorly linked to immunisation services. Prior evidence from Alberta and other settings indicates that organised school-based delivery, registry-supported follow-up, and strong provider recommendation can substantially improve coverage, while disruptions to these systems are associated with marked declines. We therefore propose that adolescent vaccine uptake should be conceptualised less as a residual behavioural problem and more as a delivery-system transition problem. Policy responses should prioritise transition-sensitive service redesign, including structured catch-up pathways, registry-linked reminder systems, provider prompts, and multilingual navigation embedded in youth-serving and newcomer services.