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.

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........

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