Human development, the substantial expansion of domestic animal populations (eg, cattle, pigs, poultry, sheep, and goats), and transformed landscapes engineered for human populations are having profound effects on the evolution and epidemiology of infectious and non-communicable diseases of all species. Intimate and rapid global interconnections mean uncontrolled infectious diseases in one part of the world can quickly threaten health across species anywhere. Although technological advances are making public health services better equipped for detecting, preventing, and controlling new infectious diseases and other health hazards, major gaps exist in the conversion of these advances into effective actions and policies at the animal–human–environment interface.1 National institutions addressing these challenges worldwide are most often not able to adequately address the large array of interconnected risks. Several human–animal–environment health approaches have been applied to improve global health security across a range of health hazards. The ongoing COVID-19 pandemic vividly shows that the emergence of a lethal pathogen of probable animal origin locally affects public health and almost every sector worldwide.
In 2001, the World Health Assembly decided that WHO will work with its member states towards preparedness and response to pandemics. The Food and Agriculture Organization of the UN (FAO), WHO, and the World Organisation for Animal Health (WOAH) support countries to implement international standards and frameworks, such as the International Health Regulations (IHR, 2005), the Terrestrial and Aquatic Codes and Manuals,2 and the Codex Alimentarius (ie, international food safety standards).3 The revised IHR came into force in June, 2007, and required all countries to develop core capacities for preventing, detecting, and responding to public health emergencies including those resulting from infectious agents that can adversely affect public health, travel, and trade worldwide. The IHR promoted building robust public health and animal health systems on the basis of good governance and implementation of internationally accepted standards.
In 2010, WHO, WOAH, and FAO launched a strategy for partnership (known as Tripartite Concept Note),4 recognising a shared responsibility in addressing health risks at the human–animal (wildlife and domestic)–environment interface, with avian influenza, rabies, and antimicrobial resistance as priorities. A worsening global climate crisis and the COVID-19 pandemic have spurred the formal inclusion of the UN Environment Programme (UNEP) into the Tripartite in March, 2022. This newly formed Quadripartite grouping of international agencies is supported scientifically by an independent One Health High-Level Expert Panel (OHHLEP)5 and other topic-specific scientific communities of practice, and is working on launching and implementing a global One Health Joint Plan of Action (2022–26). The shared views of these international organisations has contributed strongly to the mainstreaming of integrative approaches like One Health (panel 1) that contribute towards global health security, taking advantage of the legal mandate of the IHR as a driving force.23, 24 To support countries in implementing the regulations, while assessing their capacities to address public health risks, WHO developed the IHR Monitoring and Evaluation Framework (IHR MEF),25 which includes the IHR State Party Self-Assessment Annual Reporting tool for the mandatory annual reporting of the level of compliance with the IHR, and the Joint External Evaluation, which is a voluntary, external peer-reviewed assessment. The WOAH developed the Performance of Veterinary Services (PVS), a monitoring and evaluation tool assessing the performance of a country's veterinary services. However, the IHR and PVS frameworks were not sufficiently operational to support national responses in an internationally coordinated way or adequate for use during the COVID-19 pandemic. The COVID-19 pandemic has shown the weaknesses of global health security; has already resulted in multiple reviews of how institutions, tools, and global approaches assess capacities and build capabilities to address threats at the human–animal–environment interface; and has challenged the assumptions around the operational value of integrated approaches like One Health.26, 27, 28
Key messages
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One Health means interdisciplinary (among academic disciplines) and transdisciplinary (between academia and society) collaboration on health at the human–animal–environment interface leading to benefits that could not be achieved if the different sectors worked alone. Clear evidence exists of the benefits in terms of the number of human and animal lives saved and financial savings resulting from a close cooperation among different sectors across a range of hazards and operational functions. Our analysis indicates greater investment should be directed towards prevention and preparedness interventions across the social–ecological systems, in which the evidence base is most firmly established. This approach would lead to a shift of the disease control paradigm upstream, away from an overwhelming focus on surveillance and response in humans—which nowadays still predominates—to greater, more proactive investment in preventive interventions, and in integrating surveillance–response in environmental, animal, and human systems.
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One Health has a high potential to sustainably improve global health security for all by prioritising national and local capacity-building across relevant sectors and disciplines. In resource-constrained settings, this horizontal approach should first focus on endemic One Health issues across the ecosystem, including those with implications for food security, local community health needs, and hazards for which the evidence base is most strongly established, before considering emergent risks of more global concern that occur periodically.
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There are still daunting knowledge and implementation gaps that impede the full operationalisation of One Health for optimal global health security. As more evidence of its effectiveness becomes available, current and future One Health approaches should more fully integrate environmental, wildlife, and agriculture and farming issues across the social–ecological system to better address contemporary challenges like pandemic threats.
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Many national governments have started operationalising One Health in their governance and programmes, as reflected by an increasing degree of compliance with the International Health Regulations (IHR, 2005). This attention has received further impetus during the COVID-19 pandemic. The IHR have been a catalyst to embed cross-sectoral, whole-system approaches to public health emergencies but an evidence-led acceleration of implementation and expansion across a wider spectrum of hazards to the social–ecological system is needed.
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WHO, the World Organisation for Animal Health, the Food and Agricultural Organization of the UN, and the UN Environment Programme (ie, the Quadripartite) lead the One Health technical cooperation at the global level. In 2021, a global One Health High-Level Expert Panel came into operation to support the Quadripartite, help develop the One Health Joint Plan of Action (2022–26), and help advance One Health operationalisation.
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Further primary research and systematic reviews are needed to assess the effectiveness of One Health approaches for specific drivers of disease and hazard or risk categories across the social–ecological system. These studies should include analyses of trade-offs and cobenefits, cost-effectiveness, and comparisons of unisectoral versus multisectoral approaches, and include relevant outcome measures relating to animal and environmental health, in addition to those on human health security.
In this Series paper, we review the contributions of One Health approaches (ie, at the human–animal–environment interface) to improving global health security across a range of health hazards by use of methods detailed in appendix 1 (p 2). We summarise contemporary evidence assessing the incremental benefits of a One Health approach and how this evidence is reflected in reporting to FAO, WOAH, and WHO (appendices 2 and 3). We identify gaps of operationalisation that remain at the One Health interface to rapidly detect and respond to the risk of new and re-emerging infections and other health hazards. Through examples from the field, we build the case for One Health operationalisation and strengthened multisectoral coordination mechanisms (appendix 1 pp 10–17). As the IHR adopts an all-hazards approach to global health security, our Series paper has adapted the classification of hazards outlined in the WHO Health Emergency and Disaster Risk Management Framework29 to review the literature and to assess which categories of priority threats to global health security30 would benefit from a One Health approach.
After examining the evidence base of One Health in this Series paper, subsequent papers in this 4-part Series explore other dimensions that are crucial to foster a One Health approach to global health security. In the second paper in this Series, Mwatondo and colleagues31 show a method for mapping global One Health Networks, explore their proliferation, and highlight key characteristics of successful cross-sectoral collaboration. In the third paper in this Series, Traore and colleagues32 analyse current monitoring and evaluation tools for assessing health emergency preparedness capacities at the national level, and make recommendations for strengthening these capacities in line with a holistic One Health approach. In the fourth paper in this Series, Elnaiem and colleagues33 discuss the key challenges in the global and regional governance of One Health, assessing their implications for global health security and offering recommendations for addressing them.