The 9th World One Health Congress opens in Lisbon today with a question hanging over the field that is increasingly difficult to avoid: not whether One Health makes conceptual sense, but whether governments, institutions and investors can demonstrate what it is worth — and then fund it accordingly.
From 4–7 September, researchers, policymakers, practitioners and international organisations are gathering in Portugal for four days spanning One Health science, antimicrobial resistance, biosecurity, environmental health and the science–policy interface. The World Health Organization, Food and Agriculture Organization of the United Nations, United Nations Environment Programme and World Organisation for Animal Health — collectively the One Health Quadripartite — are all participating. But look closely at this year’s programme and a striking theme emerges: value, investment, financing, implementation, return on investment. The vocabulary of One Health is becoming increasingly economic, and that matters. For years, One Health has made a compelling biological argument — human health, animal health and ecosystem health are interconnected, so threats crossing those boundaries cannot be managed effectively by institutions acting entirely in isolation. The harder challenge has always been turning that principle into something governments can budget for. Lisbon may provide an important indication of how that conversation is changing.
From One Health as principle to One Health as infrastructure
The scientific rationale for One Health is well established. Zoonotic pathogens move between species. Antimicrobial resistance emerges through interconnected human, animal and environmental systems. Food production links animal health to human exposure. Climate and environmental change alter the distributions of hosts and vectors. Wildlife, livestock and people increasingly encounter one another across changing landscapes. None of this fits neatly inside a single ministry, yet government budgets generally do — human health has a budget, agriculture has a budget, environment has a budget, veterinary services have a budget, and emergency preparedness has a budget. The benefits of prevention, meanwhile, may appear somewhere entirely different from the institution that paid for it: a veterinary surveillance programme may detect a zoonotic threat before human cases occur, agricultural biosecurity may prevent losses that would otherwise become food-price pressures, environmental interventions may reduce opportunities for pathogen emergence, and public-health surveillance may prevent disruption extending far beyond the health system. The biological system is interconnected. The accounting system frequently is not. That is one reason financing One Health remains difficult.
The opening programme reflects that problem
The Congress runs across multiple scientific and policy tracks, but several sessions are particularly notable from a One Health security perspective. The Quadripartite programme includes Evaluating the Value of One Health: Results from the Quadripartite Online Course on Economic Evaluation Methods, Financing One Health: Sourcing Funding, Structuring Investments and Involving Private Sector Partners, and Building the Investment Case for One Health: Evidence and Return on Investment from Country Implementation. Other sessions focus on moving policy into national implementation, overcoming barriers to operationalising One Health, field epidemiology for biothreat reduction and strengthening One Health competencies. This is not simply a conference discussing whether sectors should collaborate. Increasingly, it is asking how we pay for collaboration, how we measure its value, how we demonstrate returns, and how we turn strategies into funded capabilities. Those are considerably harder questions — and they may also be the questions that determine whether One Health actually scales.
Financing prevention is on today’s agenda
One of the most relevant sessions takes place on the opening day. The Quadripartite and World Bank are convening Financing One Health: Sourcing Funding, Structuring Investments, and Involving Private Sector Partners, with a stated purpose that is practical: examining examples of how countries and regions are obtaining finance, structuring investment and working with partners to move One Health from planning toward funded implementation. There is also a PREZODE and World Bank session explicitly titled From Response to Prevention: Financing and Partnerships for Sustainable One Health Impact. That wording matters. The economics of biological risk are heavily skewed by timing — once a crisis occurs, expenditure becomes visible and urgent: hospitals need capacity, animals may need to be culled, vaccines or medicines must be procured, compensation may need to be paid, businesses suffer disruption, and governments mobilise emergency responses. Prevention competes for resources before any of those consequences are visible. The financial case must therefore often be made against something that has not happened yet.
The prevention problem is a counterfactual problem
Suppose a government invests in improved surveillance. The programme detects an outbreak early, the outbreak is contained, and only 50 cases occur instead of perhaps 5,000. What was the return on investment? We observe the 50 cases, the cost of surveillance and the response. What we do not observe is the outbreak that might have occurred without the investment — it exists only as a counterfactual. The same problem appears throughout prevention: a farm biosecurity programme may prevent pathogen introduction, a vaccination campaign may prevent disease amplification, a wildlife-surveillance system may identify a pathogen before spillover, an antimicrobial-stewardship programme may slow the emergence of resistance, and a mosquito-surveillance system may detect an invasive vector before it becomes established. Success frequently produces an absence — no outbreak, no hospital admissions, no livestock losses, no emergency. Economically valuing that absence is difficult. But without doing so, prevention will continue competing against interventions whose benefits are much easier to see.
The Quadripartite has already acknowledged the evidence gap
The Congress does not begin this conversation from nothing. On 25 August, shortly before delegates arrived in Lisbon, WHO highlighted a new FAO Investment Centre brief developed with WHO and WOAH examining the financial and economic returns from investing in One Health. Its message is significant: the wider benefits of One Health are increasingly recognised, but investment remains limited, and one reason is evidence. Decision-makers and financing institutions need stronger quantitative evidence demonstrating the additional value created by integrated approaches compared with conventional sector-by-sector interventions — a higher evidential bar than simply showing that an intervention worked. It requires asking whether the One Health approach produced better outcomes than the alternative, and whether those additional benefits were worth the additional resources required to create them.
The counterfactual has to be credible
This distinction is essential, because economic arguments for prevention can become misleading surprisingly quickly. Imagine a surveillance programme costing £5 million, against a catastrophic outbreak that might conceivably cost £500 million. It would be tempting to say that £5 million of prevention protected £500 million. But that is not necessarily true: perhaps the outbreak had only a 2% probability of occurring, perhaps surveillance would only reduce that probability by a fraction, perhaps other controls would have limited the outbreak anyway, and perhaps some of the £500 million estimate represents highly uncertain indirect losses. The economic argument therefore needs to distinguish between observed costs, observed outcomes, modelled outcomes, estimated probabilities and counterfactual losses avoided. Otherwise, prevention economics risks becoming advocacy dressed as analysis. The stronger argument is usually the more transparent one.
Not everything valuable has an easy price
There is another challenge. One Health produces benefits that do not fit comfortably inside conventional financial accounting — what is the monetary value of ecosystem resilience, biodiversity protected, public confidence maintained, antibiotic effectiveness preserved for future patients, a species not exposed to a novel pathogen, or institutional trust during an outbreak? Some can be estimated economically. Some can be represented through health metrics or environmental indicators. Others may resist meaningful monetisation, which does not make them valueless — it means economic evaluation needs to be careful not to confuse things we cannot easily price with things that have no value. A mature economics of One Health will probably require multiple measures rather than one universal ROI number.
Animal health may be one of prevention’s clearest entry points
The investment debate is particularly important for veterinary systems. WOAH has argued that stronger veterinary services, surveillance and cross-sector collaboration can detect and control biological threats closer to their source, which changes the economics of intervention. A zoonotic threat controlled within an animal population may avoid human illness, healthcare expenditure, agricultural losses, trade restrictions, food-system disruption and potentially much larger emergency-response costs. Yet the institution paying for veterinary capacity may not capture all of those benefits in its own budget — a classic One Health financing problem, in which the costs sit in one ledger and the benefits appear across several.
The private sector is becoming part of the discussion
The explicit inclusion of private-sector partners in the Congress’s financing discussions is also important. Governments do not bear the entire economic burden of biological threats: farmers lose animals, food businesses lose production, pharmaceutical companies invest in countermeasures, insurers absorb losses, employers experience absenteeism, supply chains experience interruption, tourism can decline, and financial institutions are exposed indirectly to agricultural and economic disruption. There is therefore a legitimate question about how prevention should be financed across public and private actors. But private financing also introduces governance questions — who determines priorities, who captures returns, who owns resulting infrastructure or data, and what happens to interventions whose social value is high but whose commercial return is low? One Health financing cannot simply mean shifting public responsibilities to private capital. It needs structures in which incentives align with public-health objectives.
The environmental pillar cannot remain decorative
UNEP’s participation is particularly important here. One criticism historically directed at practical One Health implementation is that the environmental component can receive less operational attention than human and animal health. The Congress programme gives environment and ecosystem health substantive space, including sessions on climate change, biodiversity and health, and that matters because prevention frequently begins upstream: land-use change can alter wildlife contact, climate change can shift vector ranges, pollution can influence antimicrobial resistance, and biodiversity changes can reshape ecological relationships relevant to disease emergence. Intervening at those levels may sometimes reduce risk before a conventional health system ever encounters a case. But environmental prevention also creates some of the hardest economic-evaluation problems, because benefits may be diffuse, long-term and shared across society. If Lisbon is serious about financing One Health, environmental value needs to survive contact with the spreadsheet.
A useful test for every prevention proposal
There is a relatively simple discipline that could improve many investment discussions. For any proposed prevention expenditure, it is worth asking four questions in sequence. First, what are we actually buying — not simply “surveillance” or “preparedness,” but what actual capability does the money create: more laboratories, faster diagnostics, additional veterinary personnel, more sampling, better data integration, stockpiles, vaccination coverage? Second, what changes because that capability exists — does detection occur earlier, does transmission probability fall, does response time improve, does pathogen introduction become less likely? Third, what outcomes could that change prevent or reduce — human illness, animal mortality, culling, healthcare costs, production losses, trade disruption, environmental damage? And fourth, how certain are we — which benefits have been observed, which are modelled, which depend on assumptions, and which remain speculative? That sequence is the difference between saying prevention is valuable and showing how prevention creates value.
Lisbon and the economics of prevention
For One Health Security, the timing of this Congress is particularly interesting. Our forthcoming Monthly Review No.002 is examining The Economics of Prevention, and we are developing an experimental OHS Prevention Ledger built around essentially the same problem now visible in Lisbon — tracing prevention investment through the capability it creates, the risk it reduces, and the outcomes it potentially avoids, through to economic and societal value. The intention is not to manufacture impressive ROI numbers. Quite the opposite: we want to distinguish measured evidence from modelled counterfactuals and make uncertainty visible rather than hiding it inside a headline figure. The discussions taking place in Lisbon this week therefore deserve close attention. If One Health is moving from conceptual acceptance toward serious investment planning, then the methods used to establish value will matter enormously.
What we will be watching
Three questions in particular are worth following through the Congress. First, what counts as convincing evidence of One Health return on investment? Case studies are useful, but governments making long-term spending commitments need methods capable of comparing interventions across sectors and circumstances. Second, how will benefits distributed across sectors be reflected in investment decisions — a programme paid for by agriculture may generate savings in healthcare, and traditional departmental budgeting struggles with that. Third, how will uncertainty be represented? The economics of prevention depends heavily upon probabilities and counterfactuals, and those should be visible: a range with clearly stated assumptions is often more informative than a precise-looking ROI ratio built on uncertain premises.
A Congress worth watching
The 9th World One Health Congress will discuss far more than economics — its programme spans antimicrobial resistance, environmental health, surveillance, biosecurity, wildlife health, governance, implementation and emerging science. But the prominence of investment and implementation is revealing. One Health may be entering a more demanding phase of its development. The argument that human, animal and environmental health are connected has largely been won within the One Health community. The next argument is harder: what should we actually build, what will it cost, who should pay, what measurable capability will that investment create, and ultimately, what will society gain by acting before biological risk becomes biological crisis? Those are economic questions. They are also security questions. Lisbon may not answer all of them this week. But the fact that they are moving towards the centre of the programme is itself important. For prevention to compete seriously for resources, it must become possible not only to argue that prevention is sensible — we need to become much better at demonstrating what prevention is worth.
Questions & Answers
What is the World One Health Congress?
It is a major international meeting bringing together the scientific, policy and practitioner communities working across human, animal and environmental health. The ninth Congress is being held in Lisbon from 4–7 September 2026.
Who from the international One Health system is participating?
The One Health Quadripartite organisations — FAO, UNEP, WHO and WOAH — are participating, alongside researchers, governments, practitioners, civil society and other organisations.
Why is financing important this year?
Several official sessions explicitly address financing, investment and economic evaluation. This reflects a broader challenge facing One Health: moving from strategies and political commitments toward sustainably funded implementation.
Why is prevention difficult to value?
Because many of its benefits are counterfactual. If an intervention successfully prevents an outbreak, the losses it avoided are never directly observed and must instead be estimated.
Does a high estimated outbreak cost mean prevention automatically has a high ROI?
No. The probability of the event, effectiveness of the intervention, alternative scenarios, implementation costs and uncertainty all matter. Comparing the intervention cost directly with the worst possible outbreak cost can seriously exaggerate economic returns.
What is the OHS Prevention Ledger?
It is an experimental framework being developed for One Health Security’s forthcoming Economics of Prevention review. It will trace prevention expenditure through the capability it creates, the risk reduction that capability may produce, and the resulting outcomes and costs potentially avoided — while explicitly identifying evidence quality and uncertainty.
References
- World Health Organization (2026). The 9th World One Health Congress. Lisbon, Portugal, 4–7 September 2026.
- Global One Health Community (2026). 9th World One Health Congress — Scientific and Science–Policy Programme. Lisbon, 4–7 September 2026.
- Food and Agriculture Organization of the United Nations (2026). Quadripartite at the 9th World One Health Congress.
Key Takeaways
- The 9th World One Health Congress runs from 4-7 September 2026 in Lisbon, bringing together researchers, practitioners, policymakers and international organisations.
- The Quadripartite — FAO, UNEP, WHO and WOAH — is participating across sessions covering science, policy, biosecurity, implementation and One Health capacity.
- Financing and economic evaluation are unusually prominent this year, including sessions on financing One Health, evaluating its value, and building the investment case through evidence and return on investment.
- A major challenge is the counterfactual nature of prevention: many of its benefits consist of outbreaks, losses and health consequences that do not occur.
- Credible economic evaluation should distinguish observed evidence, modelled outcomes, assumptions and uncertainty, rather than reducing prevention to an unsupported headline ROI figure.
- Cross-sector financing remains difficult because the organisation paying for prevention may not be the organisation receiving all of the resulting benefits.