A modelling study published Thursday in The Lancet Infectious Diseases by researchers from the World Health Organization has warned that the 2026 Ebola outbreak — already confirmed in the Democratic Republic of Congo and Uganda — has a nearly 70% probability of reaching South Sudan within 12 weeks. Health officials say South Sudan has some of the weakest public health infrastructure in the region and is ill-equipped to detect, contain or manage an Ebola outbreak.
What the Study Found
The outbreak, caused by the Bundibugyo strain of Ebola, was officially declared on May 15, 2026. The WHO says the virus had been circulating undetected for roughly six weeks before it was identified. As of June 22, 2026, 1,048 laboratory-confirmed cases and 267 confirmed deaths have been recorded across affected health zones in DRC.
The study estimated cross-border spillover probabilities using computer modelling across three transmission scenarios. Uganda was assigned a 94.2% importation probability — validated by 19 confirmed cases there as of early June, including five healthcare worker infections and two deaths. South Sudan was assigned a probability of 69.3%, Rwanda 8.6% and Burundi 2.0%.
Under the most likely scenario, cumulative confirmed infections were expected to reach around 990 by late June 2026, before potentially rising to 8,210 cases by September if transmission continues unchecked.
Why South Sudan Is the Greatest Concern
South Sudan is considered the next most at risk, with researchers warning it has “some of the weakest public health infrastructure in the region,” citing gaps in case management, contact tracing, safe burial, and border surveillance.
Dr Marie Rosaline Belizaire, WHO’s Emergencies Director for Africa and incident manager for the outbreak, who is also among the study’s authors, said preparedness efforts should focus urgently on South Sudan.
The Mahagi–Goli–Paidha corridor — a series of poorly monitored border crossings between DRC’s Ituri province and Uganda and South Sudan — has already served as the primary route of cross-border spread. The same geography that allowed the virus to reach Uganda provides a direct pathway toward South Sudan, where formal health infrastructure is sparse and conflict has displaced large portions of the population.
The Vaccine Gap
There is no licensed vaccine specifically for Bundibugyo ebolavirus, making prevention and control measures — such as isolating cases, contact tracing and safe burial practices — essential to stopping the spread. The authors said these measures are particularly important given the busy border crossings between DRC and neighbouring countries.
This distinguishes the 2026 outbreak sharply from recent Ebola responses in DRC, where the rVSV-ZEBOV vaccine — marketed as Ervebo — was deployed effectively against the Zaire strain. The Bundibugyo strain was first identified during a 2007 outbreak in western Uganda. The 2026 DRC outbreak is only the third time Bundibugyo has caused an identified outbreak.
A 6-week gap between the estimated index case in early April and laboratory confirmation on May 15 substantially enlarged the infectious pool before any response was possible — a critical factor the study’s authors said must inform how early outbreak detection is prioritised in the region going forward.
Uganda’s Response as a Benchmark
The study offers Uganda’s response as a model for what works. Uganda’s rapid detection and containment response, supported by district task forces activated across high-risk districts and active contact follow-up, reflects the value of previous International Health Regulations capacity investments and accumulated Ebola response experience. The authors noted this approach is applicable to South Sudan’s weaker health system.
Uganda declared its own outbreak on May 15 and imposed a temporary border closure with DRC. The fact that 20 confirmed cases have appeared in Uganda — and have been contained within manageable parameters so far — reflects a functioning health response that South Sudan would struggle to replicate.
Outbreak Trajectory and Scenarios
The researchers said the daily tally of cases and deaths is currently most closely tracking the medium transmission scenario. Under that scenario, around 8,200 cases would be recorded by September.
Imperial College London experts noted that, in recent years, Ebola outbreaks due to the Zaire strain were declared after clusters of at most 30 suspected cases and 15 to 20 community deaths. The scale of the 2026 outbreak — already past 1,000 confirmed cases — indicates the virus circulated undetected and spread for several weeks or months before the response began, making standard control measures considerably more difficult to implement.
What Researchers Are Calling For
“South Sudan must continue to reinforce infection prevention and control, rapid response capacity, and cross-border surveillance,” the researchers said. They called on all neighbouring countries to implement public health measures now, including border surveillance, contact tracing, and safe burial practices, “in the absence of a vaccine against the Bundibugyo strain.”
The researchers concluded that “spillover is no longer hypothetical,” and that the estimated probability of importation into South Sudan remains 69.3%. With 600 million dollars pledged by international donors for the DRC response, the question is whether resources can be pre-positioned in South Sudan quickly enough to detect and contain the virus if and when it arrives.
