The International Health Regulations: What Happens When an Outbreak Crosses a Border?

What happens when an outbreak crosses a border — and why the world’s most important disease-surveillance law is also one of the least understood.

A disease outbreak becomes internationally significant long before anyone uses the word pandemic. A hospital may detect an unusual cluster; a laboratory may identify an unfamiliar organism; several countries may begin reporting similar cases; a contaminated product may cross borders; a zoonotic infection may move from an animal population into people; or a virus found in one country may appear in another before investigators fully understand how it is spreading. At some point, what began as a local health event becomes something that neighbouring countries, international organisations and potentially the wider world need to know about.

The principal legal framework governing that transition is the International Health Regulations (2005), usually known simply as the IHR — one of the most important pieces of global health-security law, and one of the least well understood. The IHR do not create a world health government, nor do they give the World Health Organization authority to dictate domestic policy to countries. Instead, they create a framework of obligations through which states agree to detect significant public-health threats, assess them, notify WHO when necessary, maintain core preparedness capabilities and cooperate when risks cross borders. Their purpose is deceptively simple: international disease control works better when countries tell one another what is happening before a health emergency becomes impossible to contain. The difficult part is deciding when that point has been reached. This is the global backbone beneath our analysis of the law behind UK–EU surveillance.

The IHR are law, not merely guidance

The first important distinction is that the International Health Regulations are not simply technical recommendations issued by WHO; they are an instrument of international law. The current WHO overview describes the IHR as legally binding on 197 countries, including all 194 WHO Member States. Their purpose is to prevent, prepare for, protect against, control and respond to the international spread of disease while ensuring that measures remain proportionate to the public-health risk and avoid unnecessary interference with international traffic and trade.

That balance matters, because an international health emergency can justify substantial intervention — but it can also create incentives for countries to introduce border restrictions, trade measures or travel controls that are politically attractive but epidemiologically unnecessary. The IHR therefore attempt to do two things simultaneously: allow countries to protect health, while discouraging excessive or unjustified interference with international movement and trade. That tension runs through the entire system.

The system begins inside countries

International surveillance sounds global, but the first signal is almost always local: a clinician recognises something unusual, a laboratory identifies an unexpected pathogen, an animal or environmental surveillance programme produces a worrying result, several cases appear to be linked, and domestic surveillance systems begin assembling the evidence. The IHR require countries to maintain what are described as core capacities for surveillance and response — the ability to prevent, detect, assess, report and respond to acute public-health risks and events — and to maintain relevant capacities at international points of entry such as airports, ports and certain ground crossings.

This is one of the most important realities of global health security: WHO cannot identify every outbreak independently, so the international system depends on national systems being capable of recognising that something unusual is happening. Global surveillance therefore inherits the strengths and weaknesses of national surveillance — and if an event is missed locally, it cannot be escalated internationally.

Every unusual disease does not have to be reported

The IHR are not a system in which every infection diagnosed anywhere is automatically reported to WHO as an emergency; countries assess events. The Regulations include a decision instrument in Annex 2, which helps national authorities determine whether an event may constitute a public health emergency of international concern and therefore requires notification. The assessment considers factors such as whether the public-health impact is serious, whether the event is unusual or unexpected, whether there is a significant risk of international spread, and whether there is a significant risk of international travel or trade restrictions. Certain diseases receive particular attention because even a single case may be internationally important — but the broader principle is risk, rather than simply the name of the pathogen. This is essential for emerging infections, because the next serious international threat may not be something already sitting neatly on a statutory list; the system needs to recognise unusual biological events even before their significance is fully understood.

Countries have a communication channel with WHO

The IHR require States Parties to designate a National IHR Focal Point that is continuously accessible for urgent communications with WHO, and WHO maintains corresponding IHR Contact Points. This is operationally important: a serious outbreak is not the moment to discover that nobody knows which government office should contact Geneva, who is authorised to transmit information, or how an urgent international notification should be handled. Preparedness therefore includes communication architecture.

The 2024 amendments added another concept: National IHR Authorities, intended to strengthen implementation and coordination of IHR obligations within countries. The distinction reflects a recurring problem in health security — an international obligation may formally belong to the state, but delivering it can require ministries of health, border authorities, laboratories, emergency-management bodies, veterinary authorities, local government and many other institutions to work together. An international focal point is useful; a national system capable of feeding information into it is essential.

WHO does not have to wait passively for governments

There is another important feature of the IHR: WHO can become aware of a potential public-health event from sources other than the government of the country concerned. Media reports, scientific networks, international organisations and other forms of epidemic intelligence can all draw attention to events, and the Regulations allow WHO to seek verification from the relevant State Party when it receives information about an event that may constitute a public-health risk. This is a crucial safeguard, because a global warning system relying entirely on formal self-reporting by governments would be vulnerable to political hesitation, weak surveillance and incomplete information. Verification still requires interaction with the state concerned, however: WHO may see the smoke, but it still needs reliable information about the fire.

What actually happens when WHO is notified?

Notification does not automatically mean that WHO declares a global emergency; most internationally notified events do not become Public Health Emergencies of International Concern. Instead, information is assessed — WHO can request further details, offer technical support, compare information arriving from different countries and monitor whether the situation is changing. This is the often invisible part of international health security: the system is continuously processing signals that never become major international emergencies, which is a sign of normal function, not failure. If the event becomes sufficiently serious, however, the Director-General may consider whether it constitutes a Public Health Emergency of International Concern, or PHEIC.

What is a PHEIC?

The IHR define a Public Health Emergency of International Concern as an extraordinary event determined to constitute a public-health risk to other states through the international spread of disease, and potentially to require a coordinated international response. The phrase sounds bureaucratic, but its purpose is important: a PHEIC is essentially a formal international escalation mechanism. The WHO Director-General makes the determination, taking account of information supplied by the affected state, scientific evidence and the advice of an Emergency Committee composed of relevant experts. A declaration tells the international community that the event has crossed a significant threshold — it can mobilise attention, intensify surveillance, accelerate research, and influence funding and preparedness, and it can lead WHO to issue Temporary Recommendations about appropriate health measures. The declaration does not, however, place countries under WHO control.

WHO recommendations are not international commands

This point deserves repeating because it is frequently misunderstood. WHO cannot use the IHR to impose a lockdown on a country’s population; it cannot order a government to introduce mandatory vaccination; it cannot direct national police powers; and it cannot override national constitutions or parliaments. WHO’s own explanation of the 2024 amendments is explicit that the amended Regulations do not give WHO the power to impose health measures, lockdowns or restrictions on the population of any country. The IHR establish international obligations for states and give WHO important assessment, coordination and recommendation functions — which is not the same thing as supranational executive authority. Temporary Recommendations issued during a PHEIC are, as their name suggests, recommendations, and countries remain responsible for implementing domestic health measures. This creates a system based substantially on cooperation rather than command, which has obvious advantages for sovereignty — but it also means the speed and quality of international response depends heavily on what governments choose, and are able, to do after an international warning has been issued.

Why was the system changed after COVID?

COVID demonstrated both the importance and the limitations of the IHR. The Regulations provided the legal framework through which the outbreak was notified, assessed and eventually declared a PHEIC, yet the pandemic also exposed weaknesses in preparedness, supply chains, international cooperation, equity and the speed with which countries translated warnings into action. WHO Member States therefore began negotiating amendments, and the process concluded at the World Health Assembly on 1 June 2024, when a package of amendments was adopted by consensus; for most States Parties, those amendments entered into force on 19 September 2025. The changes do not create a completely new system — they attempt to strengthen the one already in place — and among their most significant innovations is the introduction of the concept of a pandemic emergency.

A pandemic emergency is a higher alarm

The amended IHR create a new category for particularly serious communicable-disease events. A pandemic emergency remains within the broader PHEIC framework but represents a higher level of international concern: the criteria concern communicable disease that has, or presents a high risk of having, wide geographical spread; exceeds or risks exceeding health-system capacity; causes or risks causing substantial social or economic disruption; and requires rapid, equitable and enhanced coordinated international action. This is not simply a new word for pandemic — it is an attempt to formalise a point at which the international system should recognise that an event threatens to become globally systemic. We examine that mechanism in detail in What Is a Pandemic Emergency?

One Health complicates the IHR picture

The IHR are deliberately broad: they apply to public-health risks regardless of their origin or source, which is important because serious human-health threats may begin far outside hospitals. A novel zoonotic virus may first appear in animals; a foodborne threat may first appear in food surveillance; antimicrobial resistance may be detected through wastewater; a vector-borne disease may first become visible through entomological surveillance; and a chemical or radiological incident can also have international public-health implications. This breadth makes the IHR compatible with One Health thinking. The practical problem is that the information feeding the IHR often sits inside different institutions: if veterinary surveillance identifies an unusual animal virus with plausible zoonotic potential, at what point does that become information relevant to the national IHR system? What if environmental surveillance detects a worrying resistance gene before clinical laboratories see corresponding human infections? The legal framework can accommodate public-health risks from different origins; the governance system still has to connect the signals.

Annex 2 is only as good as the information reaching it

This is where One Health becomes an operational rather than a philosophical issue. A national health authority cannot properly assess an emerging zoonotic threat if veterinary information remains within another ministry, and a potential environmental warning cannot influence international notification if nobody connects it with human-health risk. The crucial question is therefore not simply whether the IHR contain an assessment algorithm; it is which signals reach the people using it. That creates a domestic One Health requirement underneath an international legal obligation: animal-health authorities, environmental surveillance programmes, laboratories, food-safety bodies and public-health agencies need escalation pathways that allow potentially important biological information to move between sectors. Otherwise, the global system may begin too late — the same interface problem that recurs across One Health governance.

The IHR also govern the border

International disease control naturally raises questions about borders, and the IHR contain provisions relating to international traffic and designated points of entry: countries maintain public-health capacities at relevant airports, ports and ground crossings, while the Regulations establish rules affecting matters such as health documents, travellers and conveyances. The underlying philosophy is that borders should be used to manage genuine public-health risks without causing unnecessary interference with international traffic and trade — which is harder than it sounds. During uncertainty, governments face enormous pressure to be seen to act; closing a border can be politically visible, but whether it materially reduces transmission depends on the pathogen, timing and context. This is another area where governance latency matters: a border measure introduced too late may achieve little, while a measure maintained long after its epidemiological justification has disappeared can create unnecessary economic and social harm. Good governance needs to change as the biology changes.

Surveillance is not enough without capacity

Another important lesson from the IHR is that reporting obligations alone do not create health security. A country cannot notify an outbreak it cannot detect; it cannot investigate transmission without laboratories and epidemiological expertise; it cannot operate points of entry effectively without trained personnel; and it cannot implement public-health measures without functioning institutions. The Regulations therefore place substantial emphasis on core capacities: countries assess and report on their IHR implementation, while WHO provides tools, guidance and support including Joint External Evaluations and other preparedness mechanisms. This shifts the conversation from emergency response towards resilience — the most important international outbreak intervention may happen years before an outbreak begins, when a laboratory network is strengthened, a surveillance system is improved or communication responsibilities are clarified. Preparedness is often invisible until its absence becomes obvious.

The biggest vulnerability may sit between institutions

The amended IHR strengthen the formal international architecture, but the recurring One Health problem remains: outbreak information does not arrive in one perfectly organised stream. It appears in pieces — an unusual animal infection, a cluster of human cases, a wastewater signal, a genomic match, a hospital alert, an unusual pattern of international travel, a food-safety finding — and each institution sees part of the event. The effectiveness of the IHR depends on those fragments becoming a coherent national assessment quickly enough for international notification and response to remain useful, which makes the real architecture look something like:

1. Local signal
2. Sector recognition
3. Cross-sector connection
4. National assessment
5. International notification
6. WHO assessment
7. International coordination

Every transition creates an opportunity for delay.

Measuring governance latency

This suggests a useful way to evaluate IHR performance. Traditionally, we might ask whether a country complied with its notification obligations — which matters — but a more revealing question is how much time passed between the first meaningful signal and international recognition. That interval can be divided: detection latency (how long before the signal was identified), interpretation latency (how long before somebody recognised that it might be important), cross-sector latency (how long before relevant information from different systems was connected), notification latency (how long before the international system received it), and response latency (how long before the information materially changed action). This approach distinguishes legal compliance from operational performance: a notification may technically comply with the Regulations while still arriving later than it could have if domestic information systems were better connected — precisely the kind of hidden delay One Health Security should be interested in.

What should countries do differently?

The amended IHR provide an opportunity to strengthen more than formal compliance. Countries should test the complete route through which unusual biological information reaches international decision-makers, which means exercises should not begin with an obvious human outbreak conveniently waiting for notification; they should begin with ambiguity — an unexplained cluster in cattle, an unusual pathogen in wastewater, a strange genomic sequence from a food sample, a few severe infections with no known connection — and then ask how long it takes for information to cross institutional boundaries, become a national assessment and, where appropriate, reach WHO. National IHR Authorities could become particularly valuable here if they operate as genuine coordination mechanisms rather than administrative designations. The IHR system should also connect more deliberately with veterinary, food, environmental and genomic surveillance: the goal is not for every animal-health observation to become a WHO alert, but for potentially significant signals to have a clear route into the national public-health risk-assessment process.

What the IHR cannot solve

The IHR are fundamental, but they cannot solve every problem exposed by a pandemic. They do not determine how vaccines should be shared globally; they do not create manufacturing capacity; they do not resolve disputes about access to pathogen samples and sequence information; they do not eliminate inequalities between health systems; they do not replace animal-health or biodiversity law; and they do not govern every commercial supply-chain problem. This is one reason the WHO Pandemic Agreement was subsequently negotiated. The IHR principally provide an international framework for surveillance, notification, preparedness, assessment and response, while the Pandemic Agreement attempts to address a wider set of pandemic-prevention, preparedness and equity problems. Understanding this distinction matters: the two instruments are intended to complement one another, not to duplicate one another.

So what happens when an outbreak crosses a border?

There is no single dramatic moment when an international authority takes control. Instead, a series of legal and institutional mechanisms begin interacting: a country detects something unusual, its surveillance system assesses the event, and its IHR structures determine whether international notification is required; WHO receives information and may seek verification or additional evidence; international surveillance looks for related signals elsewhere; and if the threat becomes sufficiently serious, an Emergency Committee may be convened and the Director-General may determine that a PHEIC exists — or, if the much higher criteria are satisfied, that a pandemic emergency exists. WHO can coordinate, advise, alert and support; governments remain responsible for domestic action.

The entire system therefore depends on a simple but demanding principle: information must travel faster than the threat. The IHR provide the legal route. Whether the information moves quickly enough depends on everything beneath them — laboratories, surveillance, governments, trust, communication and, increasingly, the ability to connect human, animal and environmental signals. The law can require countries to build the bridge. One Health security asks whether the bridge actually works when biology begins moving across it.

Related One Health Security analysis

This piece is part of our Rules of Outbreaks series on global health law. It is the backbone companion to Who Governs a Global Outbreak? (the architecture), What Is a Pandemic Emergency? (the highest alarm) and One Pathogen, Four Legal Systems (the journey).

Correct at the time of writing (August 2026): the 2024 IHR amendments are in force; the WHO Pandemic Agreement and its PABS annex remained under negotiation.

Questions & Answers

References and further reading

1. World Health Organization. International Health Regulations (2005), as amended in 2014, 2022 and 2024 (current text since 19 September 2025).
2. World Health Organization (2024). International Health Regulations: amendments — questions and answers. 1 October 2024.
3. World Health Organization (2025). Amended International Health Regulations enter into force. 19 September 2025.
4. World Health Assembly (2024). WHA77.17 — Strengthening preparedness for and response to public health emergencies through targeted amendments to the International Health Regulations (2005). Adopted 1 June 2024.
5. World Health Organization. IHR Emergency Committees; and the Joint External Evaluation tool and national IHR core-capacity assessments.