Scenario assessment: 2026 Ebola disease outbreak caused by Bundibugyo virus in the Democratic Republic of Congo

Introduction

On May 15, 2026, the Democratic Republic of Congo (DRC) ministry of health declared an Ebola disease outbreak caused by Bundibugyo virus. On May 17, WHO declared this outbreak a Public Health Emergency of International Concern. As of October 31st, the outbreak is the second-largest Ebola outbreak on record, with 10,498 confirmed cases and 5,107 deaths reported. The largest, the 2014–2016 Ebola outbreak in West Africa, resulted in 28,610 reported cases and 11,308 reported deaths.

To inform preparedness and decision-making, CDC followed a standardized scenario assessment framework to outline three plausible scenarios for the future course of this outbreak, including implications for the region and beyond. CDC's Center for Forecasting and Outbreak Analytics (CFA), in collaboration with the CDC 2026 Ebola Response, developed these scenarios based on what is known about the current outbreak and insights from previous viral hemorrhagic fever outbreaks. This report outlines a set of indicators for each scenario and uses the latest evidence to assess which scenario best characterizes how the outbreak is expected to progress. Challenges in assessing the most likely scenario include a lack of available data on the proportion of cases detected and potential undetected chains of transmission, variation in outbreak trajectories across different health zones, and the possibility of a Bundibugyo-specific vaccine becoming available. CDC will continually evaluate the current outbreak and update this assessment as warranted.

Potential outbreak scenarios

This assessment outlines three plausible scenarios for how the outbreak could progress within the next three months (through January 2027):

• Scenario A: Outbreak is rapidly brought under control, with the rate of new cases on a clear downward trajectory. In this scenario, there is limited additional spread into new areas of DRC or to bordering areas of Uganda and/or South Sudan. Typically, cases are rapidly contained with little or no onward transmission.

• Scenario B: Outbreak continues with multiple significant clusters of transmission, with the rate of new cases not clearly declining. In this scenario, controlling the outbreak with public health interventions in all affected areas simultaneously presents significant challenges, leading to ongoing transmission within the DRC. The geographic footprint of the outbreak would not change substantially, with the overall number of health zones experiencing transmission remaining stable. Importation of cases into neighboring countries may occur, but they would be brought under control with limited secondary transmission.
  • Additional resources are needed to increase the capacity of public health response, including for rapid response to case alerts, isolation of cases, contact tracing, and medical care as the number of cases in the outbreak increases.
  • Even without exponential growth, this outbreak could last for many months.

• Scenario C: A very large, sustained outbreak with high-intensity transmission in multiple areas of DRC, with the rate of new cases continuing to increase. In this scenario, multiple densely populated areas within the DRC experience a high intensity of transmission, with potential to establish in other countries. The geographic footprint of the outbreak would likely expand, with transmission occurring in an increasing number of health zones within DRC. Importation and spread in neighboring countries are more likely in this scenario compared to Scenarios A and B.
  • In this scenario, substantial additional resources are needed to bring this outbreak under control, requiring an expanded international effort.
  • Of the three potential scenarios, exportation to other countries is most likely to occur in this scenario.

Indicators

CDC identified eight indicators to assess which scenario is most likely occurring. Indicators are not exhaustive. No single indicator or combination of indicators is required to classify the outbreak under a given scenario. The overall assessment is based on the available evidence and subject matter expert judgment.

TABLE 1. Key indicators and corresponding levels for potential outbreak scenarios, 2026 Ebola disease outbreak. Blue shading indicates the level currently assessed for each indicator as of October 30, 2026. Shading in more than one column denotes substantial uncertainty in a given indicator.

Assessment of the most likely future scenario

As of November 2nd, 2026, the most likely scenario is assessed to be Scenario C, but several indicators are consistent with Scenario B. This assessment notes substantial uncertainties in several indicators due to data gaps, namely the growth rate of the outbreak and the proportion of cases detected and isolated. No indicators were consistent with Scenario A. The factors below were considered in the assessment of the indicators:

• The current growth rate of the outbreak may have stabilized based on reported cases. However, assessments of the current overall trajectory of the outbreak do not capture the variation in outbreak growth by health zone, the influence of under-detection on growth rate, or the significant growth that has already occurred. The proportion of cases detected and changes in that proportion over time are uncertain, posing challenges to determining the true current growth rate of the outbreak.
  • While cases in some health zones have slowed, the growth rate is still increasing in others, and cases continue to spread to new health zones over time.
  • Overall, the 2026 Bundibugyo outbreak has grown more rapidly than any previous Ebola outbreak, reaching more than 5,000 cases in the first 100 days after the first case was identified.
  • Transmission probably began several months before the outbreak was detected, contributing to the rapid growth rate observed.
  • Stabilization in cases over the past several weeks does not rule out the possibility that the growth rate of the outbreak is still increasing, as there might be lags in data reporting or decreases in case reporting over time.

• As of July 12, an estimated 15–20% of cases were coming from known contacts, far below the target of 90%. This might reflect true undetected chains of transmission as well as gaps in contact tracing.
• While data is available about the percent of contacts traced and the total number of contacts identified per case, how quickly contacts are identified is not known.
  • Operational indicators on contact tracing completeness and average number of contacts identified per case remain below target levels.
• The percentage of cases currently in isolation is unknown. However, as of September 10, 2026, 67% of deaths are reported to be occurring in the community, outside of Ebola Treatment Units.
• The proportion of cases that are currently detected is not known. However, as of August 20, 2026, Africa CDC reported in comments to press that an estimated 30–40% of cases are detected.
• As of November 2nd, the DRC received 70,000 doses of Ervebo vaccine, with 50,000 allocated to frontline workers and 20,000 for a Phase 3 clinical trial, which is now underway. Multiple Phase 1 clinical trials for vaccines specific to Bundibugyo virus are under way. However, ERVEBO's efficacy against Bundibugyo virus is unclear, and currently no approved vaccine exists against Bundibugyo virus.
• As of November 2nd, a total of 67 health zones in DRC across 8 provinces have been affected, including spread to 4 new health zones in the month of October.
• Cases have been detected outside of DRC in Nigeria, Kenya, Uganda and France.
  • On October 20th, Nigeria reported a case of BVD. There have been no additional cases reported as of November 2nd.
  • The case in Kenya was believed to have traveled to Kenya from DRC via Uganda, where they passed through the country without detection. As of November 2^nd, eight further cases were detected, including an additional death. All additional cases were relatives or healthcare providers with close contact with the first infected man, and all were already in quarantine when diagnosed.
  • Cases in Uganda were also primarily imported and the last confirmed case in Uganda recovered and was released from care on July 16, 2026.
  • The case in France was imported and did not lead to any further infections. Currently, there are no reported active cases outside of DRC.

Based on this evidence, five indicators are consistent with only Scenario C, one indicator is consistent with only Scenario B, and two indicators are consistent with both Scenarios B and C. More indicators are consistent with Scenario C; however, several indicators consistent with Scenario B suggest some potential for the current outbreak to follow Scenario B. This outbreak has already become the second largest reported outbreak of Ebola on record, and, based on this and other assessments, is expected to persist for an extended period. CDC has moderate confidence in this assessment based on the extent and quality of information available, which includes significant data gaps outlined above. Changes in the outbreak or data available that could change the assessment are outlined below.

Key Uncertainties

This scenario assessment is intended to provide a high-level overview of how the outbreak could progress during the next three months (through January 2027) based on the currently available information. Several areas of uncertainty remain that could change this assessment or warrant consideration of additional scenarios including:

• The proportion of cases detected and the proportion of detected cases successfully isolated is not known, although Africa CDC and WHO have provided some estimates of case detection.
• The extent and timeliness of contact tracing is also unclear, meaning it is difficult to determine whether the currently low percentage of cases coming from a contact list is due to gaps in contact tracing failing to identify a true connection to existing transmission chains, or if many undetected chains of transmission.
• No vaccine against Bundibugyo virus has been approved; if clinical trials of existing vaccines against Ebola virus or new candidate vaccines are found to be effective against Bundibugyo virus, then the outbreak might be controlled more rapidly.

Background

Outbreak in the Democratic Republic of the Congo

On May 15, 2026, CDC received media reports regarding 265 suspected cases of Ebola, including 65 deaths (4 deaths laboratory confirmed), mainly recorded in DRC's Ituri Province in the Mongwalu and Rwampara health zones. Suspected cases were also reported in Bunia, the capital of Ituri province. On May 15, Africa CDC confirmed that the cause of this outbreak is Bundibugyo virus (Orthoebolavirus bundibugyoense), one of four strains of orthoebolavirus that can cause Ebola disease in humans.

On May 17, WHO declared this outbreak a public health emergency of international concern. Previous outbreaks in Ituri province have included the large 2018–2020 outbreak that led to 3,470 cases and 2,287 deaths from Ebola virus in DRC. That outbreak was exacerbated by a number of challenges including armed conflict, which resulted in interruptions to public health response. The largest Ebola outbreak on record, the 2014–2016 outbreak of Ebola virus in West Africa, resulted in 28,610 reported cases and 11,308 reported deaths. That outbreak was distinguished by high-intensity transmission in large urban centers.

Ebola Disease Epidemiology and Natural History

Bundibugyo virus is thought to be transmitted most commonly through direct contact with body fluids from an infected person or contact with an infected animal, possibly a bat or primate. People with Ebola disease usually start getting sick 8–10 days after exposure (range 2–21 days). Symptoms can appear suddenly and can include fever, vomiting, diarrhea, rash, and severe bleeding.

Groups considered to be at higher risk of acquiring Ebola include:

• People (including healthcare workers) caring for persons who are sick with or died from Ebola, without using adequate personal protective equipment and infection control procedures.
• People (including household or family members) having direct contact with persons who are sick with or died from Ebola, without using adequate personal protective equipment and infection control procedures.

Outbreak Scenario Assessment Methods

CDC used a standardized framework to conduct this scenario assessment. CDC subject matter experts considered past and current outbreak characteristics such as outbreak size, duration, and geographic spread to develop three outbreak scenarios, Scenarios A, B, and C, that describe qualitatively how the outbreak might progress over the next three months (through January 2027).

To assess the most likely scenario, CDC defined indicators and levels for each indicator that correspond to each scenario. CDC assessed each indicator independently by examining available evidence. The most likely future scenario(s) was then determined based on the indicator assessments. A confidence level was assigned to the assessment, based on the quality, amount, and consistency of evidence.

For more details on these methods, please see the outbreak scenario assessment methods webpage.