The Ebola outbreak that emerged in eastern Democratic Republic of the Congo and crossed into neighbouring Uganda may have been killing people for weeks before the alarm was raised. When Médecins Sans Frontières investigated in May 2026, it reported that at least 55 people had died since the beginning of April .
Authors
- Umit Seven
Marie Skłodowska-Curie Postdoctoral Fellow, University of Manchester
- Luis Martinez Juarez
Lecturer in Global Health, Humanitarian Conflict Response Institute, Manchester University
On May 17, the WHO Director-General declared the outbreak a public health emergency of international concern , signalling that countries needed to coordinate their response. By then, the virus had been circulating in a conflict-affected region where fighting had weakened the clinics, laboratories and reporting systems needed to detect and contain it.
This collision between conflict and disease extends far beyond one country. A review of previous research found that war can help infectious diseases spread by damaging healthcare, interrupting vaccination and sanitation, forcing people from their homes and preventing aid workers from reaching them. Violence can also make outbreaks harder to detect.
Spotting an outbreak early gives health authorities a better chance of containing it before it becomes a larger crisis. Yet our research suggests that countries may be least able to spot outbreaks in precisely the places where the danger is greatest.
We examined infectious-disease outbreaks reported through the World Health Organization’s disease outbreak news (Dons) between 1996 and 2024. We then compared where and when those outbreaks were reported with records of armed conflict across 236 countries and territories.
The WHO archive does not include every outbreak worldwide. It contains selected events that were detected, reported to the WHO and considered important enough to publish. Researchers have also found inconsistencies in disease names, case numbers and other details. If an outbreak goes unnoticed, or is noticed but never reported internationally, it cannot appear in the archive.
Our results therefore show patterns in reported outbreaks, not every outbreak that occurred. Even so, they suggest that conflict may affect both how diseases spread and which ones become visible to the wider world.
Many of the diseases reported more often during conflict were linked to the collapse of basic services. Reported polio outbreaks, for example, became more common during civil wars. This fits with evidence that conflict reduces vaccination coverage by displacing communities and making it dangerous or impossible for health workers to reach them.
The naturally occurring “wild” poliovirus now continues to circulate routinely in only Afghanistan and Pakistan , where insecurity has repeatedly obstructed efforts to eliminate it. Other countries can experience outbreaks linked to the weakened virus used in oral polio vaccines. These rare outbreaks occur when vaccination rates are so low that the weakened virus circulates for a long time and changes into a form capable of causing illness.
Reported cholera outbreaks followed a similar pattern, but the clearest rise came one and two years after fighting began. This may be because clean-water supplies, sanitation and healthcare deteriorate gradually during a prolonged conflict. Our study found a pattern – but it can’t prove that this was the cause.
The war in Yemen contributed to one of the largest recorded cholera epidemics in recent history . More than a million suspected cases were recorded as conflict damaged water and sanitation systems, disrupted healthcare and displaced communities.
Many of the patterns we found were strongest in sub-Saharan Africa. This may partly be because some of the diseases studied are already more common there as a result of climate, wildlife and other local environmental conditions – not conflict alone.
The pattern remained after we allowed for differences in countries’ income. But income does not tell us everything about how well a country can detect and report disease. We therefore cannot say how much of the result reflects the places where particular diseases naturally occur and how much reflects differences in reporting.
When outbreaks disappear from the records
One result ran in the opposite direction: influenza was reported less often during conflict.
History gives us little reason to assume that war prevents flu from spreading. During the first world war, mass troop movements and crowded military camps helped the 1918 influenza pandemic spread around the world. It infected an estimated 500 million people and is thought to have killed at least 50 million.
Crowding in shelters and camps could similarly help respiratory infections spread during modern conflicts. But war can also change how people travel and make it harder for them to visit a clinic. Laboratories may close, testing supplies may run out and health authorities may no longer be able to collect or share results. Flu could therefore continue spreading while becoming less visible in official records.
Tracking influenza depends on laboratories and national reporting systems connected through the WHO Global Influenza Surveillance and Response System . Damage to this network could help explain why fewer influenza outbreaks were reported during conflict.
There is another complication. Disease outbreak news is not the WHO’s main record of routine flu activity, and the types of influenza events selected for publication have changed over time. The decline could therefore reflect weaker testing and reporting, a real change in transmission, or changes in what the WHO published. Our data cannot determine which explanation is correct.
We also grouped conflicts according to how many people were killed in fighting each year. Reported outbreaks did not continue to rise as conflicts became deadlier, while reported influenza fell further.
One possible explanation is that disease monitoring continues to work during less intense conflicts but starts to collapse in the most violent ones. Yet this is not proof. Counting deaths across a whole country cannot capture every local effect of war, and changes in how diseases spread or what gets reported could also have shaped the result.
Pandemic-preparedness programmes developed since the COVID-19 pandemic have placed great emphasis on laboratories and disease-monitoring networks . But these systems still depend on something more basic: health workers who can reach people safely, clinics that remain open and institutions capable of reporting what they find. When those foundations collapse, even advanced warning systems may receive too little reliable information.
An outbreak map is often read as a picture of where disease exists. It is also a picture of where the world can still see outbreaks. In places fractured by conflict, that visibility may be fading precisely when the need for it is greatest.
