The COCCOS study protocol describes a multicentric quasi-experimental pretest-posttest evaluation of a co-designed healthcare transition program (TP) for adolescents and young adults (AYAs) with chronic conditions. The protocol responds to rising numbers of AYAs living with chronic disease and documented gaps in transition preparation that can lead to disrupted care and adverse health outcomes. The COCCOS TP was co-designed to address preparation for transfer, promote autonomy, and secure continuity of care.
The study is implemented in two Belgian university hospitals and uses a quasi-experimental design with an intervention group and a control group receiving usual care. Eligible participants are AYAs aged 17–18 years with type 1 diabetes, asthma, or obesity. Participants in the intervention arm will receive the COCCOS TP; control participants will continue with standard transitional practices at participating sites.
Primary and secondary outcomes will be measured at multiple time points (see Outcomes and measures). The study integrates quantitative effectiveness assessment, a health economic analysis from a healthcare payer perspective, and a mixed-methods process evaluation to capture implementation fidelity and contextual factors.
The COCCOS TP consists of four structured consultations delivered over 13–16 months prior to and around the time of transfer from paediatric to adult services. The consultations target transition preparation, development of self-management and autonomy, and mechanisms to support continuity of care during and after transfer. The programme was co-designed with stakeholders; specific session content, providers, and delivery modalities are described in the full protocol.
The primary outcome is transition readiness, assessed using the Transition Readiness Assessment Questionnaire. Secondary outcomes include measures of patient empowerment, medication adherence, health-related quality of life, and mental health. The protocol specifies data collection at baseline, at the time of transfer, and four months after transfer to capture short-term post-transfer outcomes.
Data collection occurs at three predefined time points: baseline (pre-intervention), at the transfer event from paediatric to adult care, and four months post-transfer. These repeated measures will allow assessment of within-subject changes over the intervention period and early post-transfer trajectory for primary and secondary outcomes.
The protocol includes a cost-effectiveness analysis conducted from a healthcare payer perspective. Effectiveness will be expressed using quality-adjusted life years (QALYs) to permit comparison with other interventions. The economic evaluation aims to provide preliminary estimates of the incremental costs and outcomes associated with implementing the COCCOS TP compared with usual care.
A mixed-methods process evaluation is embedded within the study to examine implementation fidelity, acceptability to AYAs and providers, and contextual factors influencing delivery. The process evaluation will use observations, surveys, and interviews to capture quantitative and qualitative data on how the TP is delivered in real-world clinical practice and to identify barriers and facilitators to implementation.
The study protocol is registered on ClinicalTrials.gov under identifier NCT07145671. The published protocol reports that the authors have declared no competing interests. As an open-access protocol, results and materials are intended to inform future implementation and research; plans for dissemination and next steps are described in the full article.
The COCCOS study will provide feasibility and preliminary effectiveness data for a co-designed TP for AYAs with chronic conditions in routine clinical settings. By integrating clinical outcomes, economic evaluation, and a process evaluation, the protocol targets key evidence gaps in transition-care research. Results are intended to guide refinement of the programme and the design of a future large-scale trial to support sustainable, patient-centred transition care for AYAs with type 1 diabetes, asthma, and obesity.