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Scientists comment on the World Health Organisation declaring the Ebola disease outbreak in the Democratic Republic of Congo is determined as a public health emergency of concern (PHEIC).
Dr Daniela Manno, Clinical Assistant Professor at the London School of Hygiene & Tropical Medicine (LSHTM), said:
How concerning is this development?
“This is a concerning outbreak for several reasons. First, the number of suspected cases reported before confirmation suggests transmission may have been ongoing for several weeks before the outbreak was formally recognised. Second, the outbreak is occurring in a region affected by insecurity, population displacement, and high population mobility, all of which can complicate surveillance, contact tracing, and delivery of healthcare.
“A previous Ebola outbreak affecting North Kivu and Ituri provinces between 2018 and 2020 lasted for nearly two years, with insecurity and community mistrust repeatedly disrupting contact tracing, vaccination, and response activities.
“In addition, the outbreak is now thought to becaused by Bundibugyo virus, a rare Ebola-causing virus for which there are currently no licensed vaccines or therapeutics specifically approved. There are also no vaccines in late-stage clinical development that could be readily deployed during the outbreak.
“However, it is important to emphasise that DRC has extensive experience responding to Ebola outbreaks, and outbreak response capacity is significantly stronger today than it was a decade ago.
What is a Public Health Emergency of International Concern (PHEIC)? How does this change our understanding of the situation or the public health response?
“A Public Health Emergency of International Concern, or PHEIC, is the highest level of international public health alert that WHO can declare under the International Health Regulations.
“A PHEIC does not mean the outbreak has become a global pandemic. Rather, it reflects that the event is considered serious enough to require coordinated international action, enhanced surveillance, resource mobilisation, and cross-border collaboration.
“In practical terms, the declaration helps mobilise international attention, funding, technical support, and coordination between countries and public health agencies.
How concerning is this? When was the last time a PHEIC was declared for Ebola?
“WHO previously declared a PHEIC during the large Ebola outbreak in North Kivu and Ituri provinces in DRC between 2018 and 2020, and before that during the 2014–2016 West Africa Ebola epidemic.
“The current declaration reflects concern about the operational complexity of the outbreak, including insecurity, population movement, delayed detection, and the involvement of Bundibugyo virus disease, for which there are currently no licensed vaccines or therapeutics and no vaccines in advanced clinical development that could be readily deployed during the outbreak.
The WHO say it does not meet the criteria of a pandemic emergency. What is the difference between a PHEIC and a pandemic emergency?
“A PHEIC is a formal legal mechanism under the International Health Regulations designed to trigger international coordination and support for serious public health events.
“A pandemic refers to sustained global spread of a disease across multiple countries or continents.
“Ebola outbreaks can be extremely serious and devastating locally and regionally, but Ebola does not spread in the same way as respiratory viruses such as influenza or COVID-19 and is generally much less transmissible. Transmission usually requires direct contact with bodily fluids or contaminated materials from an infected person, which makes sustained global spread much less likely.
Do we know any more about the strain causing this outbreak and does that affect the response?
“Current evidence suggests the outbreak is caused by Bundibugyo ebolavirus (BDBV), a rare Ebola-causing virus previously identified in only two documented outbreaks, in Uganda in 2007 and DRC in 2012.
“This is important because currently licensed vaccines and therapeutics developed for Ebola virus (formerly Zaire ebolavirus) are not expected to provide protection against Bundibugyo virus disease.
“As a result, response efforts rely heavily on classical public health measures such as rapid case detection, isolation, contact tracing, infection prevention and control, safe burials, and community engagement. These measures were critical in eventually controlling the 2014–2016 West Africa Ebola epidemic, the largest Ebola outbreak ever recorded, and if implemented rapidly and effectively they can also help control this outbreak.
Any other comments?
“This outbreak highlights both the progress and the remaining gaps in global epidemic preparedness. Considerable advances have been made in Ebola surveillance, diagnostics, outbreak response systems, vaccines, and therapeutics over the past decade. However, preparedness remains uneven across different filoviruses, particularly for rarer Ebola-causing viruses such as Bundibugyo ebolavirus.
“It also highlights how insecurity, displacement, and fragile health systems can continue to complicate outbreak response efforts, even when scientific tools and public health expertise are available.
Dr Anne Cori, Associate Professor in Infectious Disease Modelling, School of Public Health – Faculty of Medicine, Imperial College London, said:
How concerning is this development?
“The confirmation of the causative agent as Ebola Bundibugyo on Friday 15th of May 2026 was critical to be able to characterise the threat and use appropriate diagnostic and control strategies. However, it is concerning given there are currently no vaccines or treatments available. There is limited scientific evidence on this Ebola species as there are only two historical outbreaks recorded. These point to a highly lethal disease with an estimated 1 in 3 cases dying.
“The detection of two cases in Uganda reinforces the significance of the event to the region. In this context, the declaration by the WHO of a Public Health Emergency of International Concern (PHEIC) will help to mobilise and coordinate the resources necessary to mitigate the epidemic.
What is a Public Health Emergency of International Concern? How does this change our understanding of the situation or the public health response? How concerning is this? When was the last time a PHEIC was declared for Ebola?
“A PHEIC is an official declaration made by the WHO under the International Health Regulations, recognizing the international nature of a public health threat. It aims to help mobilise attention and resources, and coordinate response efforts at international level. The last PHEIC for an Ebola outbreak was declared in July 2019 during the 2018-20 Ebola epidemic in the North Kivu province of the Democratic Republic of the Congo (DRC). At the time, the PHEIC was declared a year into the outbreak after it reached the urban area of Goma, threatening to spread internationally to nearby Rwanda. The current epidemic already comprises confirmed cases across both DRC and Uganda which likely influenced the declaration of a PHEIC as its focus is really the international nature of the threat.
The WHO say it does not meet the criteria of a pandemic emergency. What is the difference between a PHEIC and a pandemic emergency?
“A pandemic emergency would signal a threat to the entire world, whilst a PHEIC highlights a threat to multiple countries but not necessarily a global threat. Ebola is not an airborne virus, it is transmitted through contact with the bodily fluids of an infected individual which requires relatively close contact and makes it harder to spread globally.
Do we know any more about the strain causing this outbreak and how does that affect the response?
“Historically, there have been two documented outbreaks of Ebola Bundibugyo. These outbreaks in 2007 (Uganda) and 2012 (DRC) reported less than 200 cases overall. The relatively low number of cases historically has limited the ability to generate scientific evidence on this virus. Existing evidence suggests that, similar to other Ebola species, Bundibugyo causes a very severe infection with about one in three cases dying. Control strategies are similar to those against other Ebola species, namely community engagement, active case finding and isolation, tracing and quarantining of contacts, personal protective equipment to protect health care workers and carers, and safe burials to avoid transmission during funerals. Documenting the clinical presentation and timeline of cases in the ongoing epidemic is critical to improve the evidence on this virus and adjust control measures accordingly.”
Prof Emma Thompson, Clinical Professor of Infectious Diseases and Director of the MRC–University of Glasgow Centre for Virus Research, University of Glasgow, said:
“The current outbreak in DRC and Uganda is caused by the Bundibugyo virus, a member of the species Orthoebolavirus bundibugyoense, closely related to Ebola virus (species Orthoebolavirus zairense).
“There are several reasons for concern.
“First, reports that initial GeneXpert Ebola testing was negative suggest that the outbreak may have gone undetected for some time, with early diagnostic blind spots delaying recognition.
“Second, infections in healthcare workers are a serious warning sign in any filovirus outbreak, because they indicate unrecognised transmission in healthcare settings and gaps in infection prevention and control.
“Third, the identification of cases in Kinshasa and Kampala, hundreds of kilometres from Ituri province, shows that the virus has already moved through human mobility networks before full containment was in place.
“Bundibugyo virus has caused two previously recognised outbreaks. The first was in Bundibugyo District, Uganda, in 2007–2008, with 131 reported cases and 42 deaths, and a case fatality proportion of 34–40%. The second was in Isiro, Democratic Republic of the Congo, in 2012, with 38 laboratory-confirmed cases and 13 deaths, although wider outbreak reports including probable and suspected cases gave higher totals. These figures are lower than the case fatality rates seen in many outbreaks caused by Ebola virus, but they are still extremely serious. Bundibugyo virus disease is not a mild infection.
“There is a licensed vaccine that targets Ebola virus from the species Orthoebolavirus zairense (rVSV-ZEBOV). Experimental non-human primate work suggests that rVSV-ZEBOV may provide partial heterologous protection against Bundibugyo virus, but this cannot be assumed to translate into reliable protection in people during an outbreak. Adenovirus- and MVA-vectored vaccine platforms may offer broader possibilities, particularly where multivalent constructs are used, but recent immunological data suggest that some licensed or advanced platforms still induce responses that are predominantly directed against Ebola virus rather than broadly cross-reactive across all ebolaviruses. In plain terms, we do not currently have a proven, licensed, Bundibugyo-virus-specific vaccine available for outbreak control and further urgent research is required.
“The same applies to therapeutics. Approved monoclonal antibody treatments such as Inmazeb and Ebanga were developed for disease caused by Ebola virus, not Bundibugyo virus, and their efficacy against other ebolaviruses has not been established. There are promising experimental broad-spectrum antibodies, but these are not yet a substitute for rapid detection, high-quality supportive care, infection prevention and control, and contact tracing.
“The immediate priorities are therefore practical and scientific: Bundibugyo-virus-capable diagnostics, rapid genomic sequencing, strong infection prevention in healthcare settings, safe clinical pathways, contact tracing, community engagement, and treatment centres able to deliver high-quality supportive care. Genomic sequencing is particularly important because it can confirm the virus species, identify whether cases are linked, reconstruct transmission chains, and detect whether the outbreak reflects sustained human-to-human transmission or multiple introductions.
“This outbreak also highlights a persistent weakness in epidemic preparedness. We tend to build tools around the best-known outbreak pathogens, but rarer viruses such as Bundibugyo virus can still cause severe disease and international spread. Sustained investment in high-containment laboratories, diagnostic development, genomic surveillance, vaccine platforms, therapeutics and international research partnerships is essential. These capacities cannot be assembled at speed once an outbreak is already moving.”
Dr Natsuko Imai, Research Lead in Epidemics and Epidemiology at Wellcome, said:
“While the global risk remains low, this evolving situation is concerning. The Bundibugyo ebolavirus is less common than other strains, with this marking only the third recorded outbreak. Unlike for the Zaire ebolavirus, there are no approved vaccines or therapeutics, and limited diagnostics relying on specialist labs, making it difficult to assess the true scale of its spread.
“Public health officials in the area have significant experience dealing with Ebola outbreaks, but rapid, coordinated response is essential. Global collaboration to strengthen active surveillance, contact tracing, infection prevention and control measures, as well as community engagement and safe and dignified burials are vital for containing the outbreak and protecting the communities at risk in the DRC, Uganda, and neighbouring countries.”
Dr Amanda Rojek, Associate Professor of Health Emergencies, Pandemic Sciences Institute, University of Oxford, said:
“The declaration of a PHEIC does not immediately change the reality on the ground. What it does do is signal to the international community the need to pay attention to this outbreak and support a well-coordinated response.
“It does not mean the outbreak is globally uncontrollable, but it does reflect that the situation is complex enough to require international coordination. There are already major challenges to controlling this outbreak. Some cases are in remote regions that are difficult for healthcare teams to access safely, while cases in capital cities create different risks. The simultaneous activity in DRC and Uganda also increases the importance of cross-border coordination and preparedness.
“Bundibugyo is a less commonly encountered strain of Ebola. There have been two previous outbreaks, one in Uganda and one in DRC, both more than a decade ago. Since then, we have significantly improved the quality of supportive care provided to patients with Ebola, and much of that experience will still be relevant here.
“Unfortunately, Bundibugyo has fewer proven countermeasures than Zaire ebolavirus, where vaccines have been highly effective in controlling outbreaks. Work is now urgently underway to determine which experimental treatments and vaccines should be prioritised for testing.
“Importantly, this declaration should also be seen as evidence that the international system is responding earlier and more proactively than in previous outbreaks. There are now much stronger surveillance systems, diagnostics, treatment trial networks, and regional preparedness mechanisms than existed a decade ago. Both DRC and Uganda also have substantial experience managing Ebola outbreaks.”
Prof Trudie Lang, Professor of Global Health Research, University of Oxford, said:
This latest Ebola outbreak, involving the Bundibugyo ebolavirus (BDBV) strain, presents several factors that together make it a significant public health concern and have driven the WHO’s decision to classify the situation as a Public Health Emergency of International Concern. The outbreak meets these criteria through its potential for cross-border spread, the operational challenges affecting detection and response, and the need for coordinated international support.
“Teams in the Democratic Republic of Congo are reporting serious challenges in the most vulnerable and affected areas, where access is difficult and laboratory confirmation of cases remains limited. As a result, detection and surveillance have been sporadic and complex, meaning cases may go undetected for periods of time before being identified and investigated.
“One of the most significant concerns is that this outbreak involves the Bundibugyo ebolavirus (BDBV) strain, a form of Ebola for which we do not currently have licensed vaccines available.
“The outbreak is occurring in a region that continues to experience the impacts of previous disease outbreaks. Many of the affected areas are mining towns with highly mobile and transient populations. This mobility increases risk as people move between communities and across borders. Ongoing local political instability and insecurity further complicate response efforts and access to affected populations.
“Importantly, many of the same public health and healthcare teams responding to this Ebola outbreak are also continuing to manage the ongoing mpox outbreak, which remains present and continues to transmit from person to person in parts of the region. This creates a layered emergency response environment, placing additional pressure on already stretched laboratory systems, surveillance networks and frontline health services. These overlapping outbreaks highlight the extraordinary challenges faced by teams working in these communities and border towns, where population movement, insecurity and competing health priorities can make outbreak detection, containment and continuity of response especially difficult.
“The immediate priorities are an urgent need for locally led and delivered community engagement effort to reduce transmission, strengthen trust and support early care-seeking and reporting. Second, laboratory systems and access to detection capabilities must be strengthened to enable faster case identification, more effective surveillance and improved outbreak monitoring.
“This response also depends upon strong cooperation, transparent information sharing and interoperable systems so that the situation can be understood and managed effectively across local, national and regional levels. There is strong local expertise and significant regional capacity already engaged in the response. Africa CDC and WHO have moved swiftly and are highly active, and response coordination and collaboration are robust and underway. Building and connecting these existing strengths and systems will be essential to bringing the outbreak under control.
“Beyond community engagement and strengthening detection capabilities, the immediate major challenge is to rapidly evaluate a vaccine candidate within the outbreak setting so that strategies such as ring vaccination can be considered and deployed if proven effective. Advancing this work quickly and safely may prove critical to limiting further spread and protecting vulnerable communities and health workers.”
Some previous comments on the outbreak can be seen here: https://www.sciencemediacentre.org/expert-reaction-to-ebola-outbreak-in-democratic-republic-of-the-congo/
Declared interests
Dr Daniela Manno: Dr Daniela Manno has previously worked on Ebola vaccine clinical trials and outbreak preparedness research in Sierra Leone, Tanzania, and the Democratic Republic of Congo.
Dr Anne Cori: AC has received research funding from WHO and GAVI the Global Vaccine Alliance Initiative to evaluate the benefits and costs associated with the global Ebola vaccine stockpile. She has received consulting fees from Munich Re for work on Evaluating the likelihood and severity of pandemics.
Prof Emma Thompson: “Professor Thomson is Director of the MRC–University of Glasgow Centre for Virus Research and is involved in research collaborations in Uganda relating to viral surveillance, genomics and emerging infectious diseases. She has received research funding from UKRI, MRC, NIHR and other public and charitable funders. She has no relevant personal financial interests relating to Ebola vaccines or therapeutics.”
Dr Natsuko Imai: No COI
Dr Amanda Rojek: I’m the clinical lead for the WHO sponsored PARTNERS trial (the treatment trial in the region).
Prof Trudie Lang: No conflicts of interest