The Lancet Infectious Diseases: Growing DRC Ebola outbreak has already spread to Uganda with 70% chance of reaching South Sudan, new modelling study suggests

• New estimates suggest that the current Bundibugyo ebolavirus outbreak in the Democratic Republic of Congo (DRC) continues to grow and has already spread to Uganda, with a nearly seven-in-ten chance of the virus reaching South Sudan.
• As of 22 June 2026, there have been 1,048 laboratory-confirmed cases and 267 deaths recorded in DRC.
• The virus spread undetected for six weeks before being identified by WHO and officially declared a public health emergency. Early suspected case counts peaked at 1,077 before being revised downward once laboratory tests confirmed that many of those patients had other illnesses, not Ebola.
• In the absence of a vaccine against the Bundibugyo strain, the authors say neighboring countries should implement public health measures now, such as border surveillance, contact tracing, and safe burial practices, while DRC’s intensified response is showing early signs of slowing transmission. 

A rare strain of Ebola that began spreading undetected in eastern Democratic Republic of Congo (DRC) in early April 2026 has now confirmed transmission in Uganda and is potentially on course to reach South Sudan, according to a new modelling study from the World Health Organization (WHO) published in The Lancet Infectious Diseases journal.
 
The current outbreak, caused by Bundibugyo ebolavirus, was officially declared on 15 May 2026 [1]. As of 22 June 2026, 1,048 laboratory-confirmed cases and 267 confirmed deaths have been recorded across affected health zones in DRC. Early suspected-case counts peaked at 1,077 on 26 May 2026 before being revised downward once laboratory tests confirmed that many of those patients had other illnesses, not Ebola. WHO declared a Public Health Emergency of International Concern (PHEIC) on 17 May 2026 [2], the highest level of international health alert. According to the study, retrospective investigations indicate that transmission began in early April 2026. The six-week delay between the estimated first case and official confirmation suggests the virus was spreading undetected through communities in a region already destabilised by conflict, displacement, and limited healthcare access.
 
Bundibugyo ebolavirus is one of several strains of the Ebola virus. It was first identified during a 2007 outbreak in western Uganda and caused a second outbreak in the DRC in 2012. Compared to the more familiar Zaire strain, which was responsible for the 2014–2016 West African epidemic [3], the Bundibugyo strain tends to have a slightly lower mortality rate and is less transmissible. However, it still causes severe haemorrhagic fever, kills a significant proportion of those infected, and spreads through direct contact with the bodily fluids of sick or deceased people.
 
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 public health measures to stop the spread. The authors say these measures are particularly important given the busy border crossings between DRC and neighboring countries like Uganda and South Sudan.
 
Researchers used computer models to simulate how the outbreak might grow under three different scenarios: low, central (most likely), and high transmissibility. The study estimates that under the most likely (central) scenario, cumulative confirmed cases were projected to reach around 990 by late June 2026, with 174 deaths, and around 8,210 by September 2026 if transmission is merely sustained. As of 15 June 2026, 837 confirmed cases have been recorded, consistent with the central scenario. The low scenario projects around 870 confirmed cases by late June and 160 deaths. A worst-case high scenario projects the outbreak could surpass 66,000 confirmed cases by September if control measures lapse. However, the authors note that the rate of new cases in recent weeks suggests that the outbreak is more likely to follow the lower-to-central end of these projections than the worst-case scenario.
 
As of 22 June 2026, 20 confirmed Ebola cases and two confirmed deaths have been detected in Uganda, including five infections among healthcare workers. Some of these cases were brought across the border from DRC, while others were caught locally from those individuals. Uganda has been able to identify and respond to cases quickly, drawing on its experience managing previous Ebola outbreaks and the public health systems it has built up over many years.
 
The researchers now identify South Sudan as the most urgent preparedness priority, estimating a nearly seven-in-ten (69.3%) chance that at least one case will arrive there within the 12-week modelling timeline. South Sudan also has some of the weakest public health infrastructure in the region, with known gaps in case management, contact tracing, safe burial, and border surveillance. Rwanda (8.6%) and Burundi (2.0%) remain at comparatively low risk. However, the study authors note that the risk can still increase depending on detection capacity, travel patterns, and the speed of each country's response systems. 
 
The authors note some limitations of this study. The projections are based on a mathematical model calibrated to the most recent confirmed case count, so if that figure changes as more test results come in, the projections may shift accordingly. The model also treats the affected population as uniform and cannot fully account for differences between areas in terms of geography, access, or how effectively control measures are working on the ground. Estimates of how many people cross the border informally each day are also uncertain. The authors stress that these findings should be treated as an early situational assessment intended to drive proactive preparedness, rather than precise predictions, and that the projections will be updated as more verified data become available.

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