Exploring a One Health approach to sustainability with international One Health and Global Health Security experts - differences, similarities and trade-offs between sectors.

Sustainability in global health remains inconsistently defined and operationalised across human, animal, and environmental health sectors. As the One Health approach gains global traction-particularly in addressing complex, 'wicked' health problems such as pandemics, antimicrobial resistance, and ecosystem degradation-there is a growing need for shared conceptualisations of sustainability to support cross-sectoral collaboration and ultimately, long-term impacts. This study explores how One Health and health security experts from diverse disciplines understand and construct the meaning and determinants of sustainability. We conducted a qualitative study underpinned by the Social Construction Framework (SCF) through semi-structured interviews with 29 global experts from human, animal, and environmental health domains. Participants were purposively sampled from key technical advisory bodies, including the One Health High-Level Expert Panel, the World Bank Pandemic Fund, and the Quadripartite. Data were collected via online interviews between July 2023 and March 2024, transcribed verbatim, and analysed thematically using an inductive approach. Participants offered multi-dimensional definitions of sustainability; they distinguished between process-oriented (e.g., institutional longevity, financing, local ownership) and outcome-oriented (e.g., ecological regeneration, intergenerational well-being) views. Human health experts emphasised health system continuity, while animal health participants highlighted economic and disease control outcomes. Environmental experts framed sustainability around planetary resilience and equity. Cross-sectoral convergence was found on key determinants: political commitment, stable financing, workforce capacity, community ownership, and adaptability. Our findings underscore that sustainability in One Health is a socially constructed and sectorally influenced concept. Differences in framing, deservingness, and measurement priorities reflect different sectoral mandates, but also reveal potential trade-offs and synergies. To operationalise One Health effectively, an integrated sustainability framework is needed - one that aligns sectoral priorities, recognises diverse metrics, and fosters long-term, adaptive collaboration. This study provides an empirical basis for shaping such a framework, rooted in the lived experiences and perspectives of global experts.