The Bundibugyo Ebola virus outbreak in the Democratic Republic of the Congo (DRC) and Uganda is continuing. Bundibugyo virus causes a disease that kills 30%-50% of people it infects, and no approved treatments or vaccines are available. As of June 17, 2026, over 900 cases of Ebola have been reported. As the full scope of the outbreak remains unknown, it is difficult to estimate how long the outbreak could last.
Understanding the virus
Bundibugyo is one of five identified types of Ebola virus. The strain that is more commonly known is the Zaire strain, which recently caused major outbreaks in 2014 and 2018. This group of viruses circulates in animals and occasionally spills over to people. Once a person is infected, the virus spreads to other people through direct contact with body fluids, including blood, urine, saliva, feces, vomit, semen, amniotic fluid and breast milk. It can also spread by exposure to body fluids even after a person has died. Spread may be through close contact, such as exposure to respiratory secretions, or by touching objects contaminated with the virus. For more details on the infection, check our webpage “Ebola: The Disease and Vaccine.”
Existing Ebola vaccines
While two vaccines are available globally for the Zaire strain of Ebola virus, those vaccines have not been studied for effectiveness against Bundibugyo. The vaccine for the Zaire strain is a live, weakened viral vaccine in which a harmless vesicular stomatitis virus (VSV) has been altered to include the gene for the Ebola virus surface protein. As the vaccine virus reproduces, it makes the Ebola virus protein too, causing our immune system to make a protective immune response without causing Ebola disease.
Vaccine development began in the late 1970s, but due to the rarity of outbreaks, there had been little urgency in development, and any vaccine would have been difficult to test. In 2014, the scope of an Ebola outbreak in West Africa created the necessary urgency, and multiple vaccines were tested in phase 1 clinical trials. However, the clusters of cases still made it difficult to use traditional clinical trial designs to complete the studies needed for licensure. Eventually a ring-vaccination trial design was employed to get the necessary data. In this design, rather than a clinical trial occurring in a particular geographic region, it was conducted in rings around contacts. Specifically, when a case was identified, contacts of that person were identified and vaccinated. Likewise, contacts of those vaccinated individuals (“contacts of contacts”) were also vaccinated. Based on the results of the ring-vaccination trial, the first Ebola vaccine was approved by the Food and Drug Administration in the U.S. in December 2019.
Check out Ebola: The Journey to a Vaccine excerpted from our 30-minute film, Marion Gruber: Preparedness Is Prevention to learn more about the development and clinical trials of the first U.S.-approved Ebola vaccine.
The other globally available Ebola vaccine for the Zaire strain is a two-dose regimen, with each dose being delivered using different viral vectors. This regimen requires that the doses be separated by eight weeks for a prime-boost effect on the immune system. As such, this vaccine is less useful in an outbreak situation.
Resolving the Bundibugyo outbreak
At this time, scientists are working on three candidate vaccines that will need to be developed and studied in clinical trials.
Candidate vaccines
Scientists already know that people gain protection to the virus by making an immune response to a protein that sits on the surface of the virus, so that is the target for vaccination. Currently, three different approaches are being pursued:
- Recombinant VSV vaccine: This approach uses the same design as the existing Zaire Ebola virus vaccine that protects against the Zaire strain, known as Ervebo. This is the vaccine that is approved for use in the U.S. This vaccine strategy delivers the gene for the target protein via a carrier virus that does not cause disease in people, in this case a recombinant version of VSV. The existing vaccine has been used successfully in two outbreaks and in preventive campaigns.
- ChAdOx viral vector vaccine: This vaccine uses the same technology as the Oxford/AstraZeneca COVID-19 vaccine. The gene for the target protein is inserted into a chimp adenovirus that can no longer replicate. When the vaccine is administered, cells make the adenovirus proteins as well as the target protein. This type of vaccine can be manufactured quickly, which offered an advantage during the COVID-19 pandemic and will also be important in this situation. In contrast to the VSV platform, where there are data and experience with the Zaire ebolavirus, no candidate Ebola vaccines have been tested using this platform, so pathogen-specific data are limited.
- mRNA vaccine: Vaccines using mRNA technology were first licensed during the COVID-19 pandemic. Like the viral vector vaccines, mRNA vaccines offer the advantage of short production timelines. These vaccines deliver mRNA for the target protein so that the recipient’s own cells produce the protein against which an immune response is mounted. To see more about how mRNA vaccines work, check this animation. Although this animation is specific for COVID-19 vaccines, the processing and development of immunity works the same way regardless of the specific mRNA delivered.
Getting to approved vaccines
While time is critical in the development of new vaccines, plans for the clinical trials are still being finalized. As of mid-June 2026, we know the following:
- Just as Operation Warp Speed (OWS) worked in the U.S. during the COVID-19 pandemic, funds have been committed to fast-tracking the three candidate vaccines in the hope that at least one will prove safe and effective. Whereas the U.S. government funded the work of OWS, two groups that work internationally have stepped up to support this effort. The Coalition for Epidemic Preparedness (CEPI) has committed at least $60 million to support manufacturing materials, preclinical and phase 1 testing, and simultaneous manufacturing of candidate vaccines. The second group, Gavi (Global Alliance for Vaccines and Immunizations), has made $40 million available to support manufacturers in increasing production capacity. These combined efforts will ensure that if one of the vaccines is demonstrated to be safe and effective, doses can be rapidly deployed.
- Various globally based governmental and scientific partners are working to ensure ethical and safe clinical trials. The World Health Organization (WHO), the governments of the currently impacted countries, the Africa Centres for Disease Control and Prevention (Africa CDC), as well as others are collaborating to ensure that the clinical trials are developed and implemented to assess safety and efficacy while also adhering to ethical standards. Global initiatives such as this follow the WHO R&D Blueprint, aimed at responding to pressing epidemiologic situations and fast-tracking processes to ensure the availability of effective tests, vaccines and medicines. While the processes are designed to move quickly, they still abide by the ethical and scientific principles important in research and development.
- Final trial designs, including which candidate vaccines are tested in phase 3 trials, will depend on early data.
A viable vaccine is still at least months away, which means that in the short term, the primary tools for containment will be those that have historically formed the backbone of public health: contact tracing, isolation, and infection prevention in healthcare settings. In this case, safe burial practices as well as ongoing community engagement and trust building will also determine the effectiveness of current containment efforts and future acceptance of vaccines.
Resources
The Bundibugyo Ebola virus outbreak in the Democratic Republic of the Congo (DRC) and Uganda is continuing. Bundibugyo virus causes a disease that kills 30%-50% of people it infects, and no approved treatments or vaccines are available. As of June 17, 2026, over 900 cases of Ebola have been reported. As the full scope of the outbreak remains unknown, it is difficult to estimate how long the outbreak could last.
Understanding the virus
Bundibugyo is one of five identified types of Ebola virus. The strain that is more commonly known is the Zaire strain, which recently caused major outbreaks in 2014 and 2018. This group of viruses circulates in animals and occasionally spills over to people. Once a person is infected, the virus spreads to other people through direct contact with body fluids, including blood, urine, saliva, feces, vomit, semen, amniotic fluid and breast milk. It can also spread by exposure to body fluids even after a person has died. Spread may be through close contact, such as exposure to respiratory secretions, or by touching objects contaminated with the virus. For more details on the infection, check our webpage “Ebola: The Disease and Vaccine.”
Existing Ebola vaccines
While two vaccines are available globally for the Zaire strain of Ebola virus, those vaccines have not been studied for effectiveness against Bundibugyo. The vaccine for the Zaire strain is a live, weakened viral vaccine in which a harmless vesicular stomatitis virus (VSV) has been altered to include the gene for the Ebola virus surface protein. As the vaccine virus reproduces, it makes the Ebola virus protein too, causing our immune system to make a protective immune response without causing Ebola disease.
Vaccine development began in the late 1970s, but due to the rarity of outbreaks, there had been little urgency in development, and any vaccine would have been difficult to test. In 2014, the scope of an Ebola outbreak in West Africa created the necessary urgency, and multiple vaccines were tested in phase 1 clinical trials. However, the clusters of cases still made it difficult to use traditional clinical trial designs to complete the studies needed for licensure. Eventually a ring-vaccination trial design was employed to get the necessary data. In this design, rather than a clinical trial occurring in a particular geographic region, it was conducted in rings around contacts. Specifically, when a case was identified, contacts of that person were identified and vaccinated. Likewise, contacts of those vaccinated individuals (“contacts of contacts”) were also vaccinated. Based on the results of the ring-vaccination trial, the first Ebola vaccine was approved by the Food and Drug Administration in the U.S. in December 2019.
Check out Ebola: The Journey to a Vaccine excerpted from our 30-minute film, Marion Gruber: Preparedness Is Prevention to learn more about the development and clinical trials of the first U.S.-approved Ebola vaccine.
The other globally available Ebola vaccine for the Zaire strain is a two-dose regimen, with each dose being delivered using different viral vectors. This regimen requires that the doses be separated by eight weeks for a prime-boost effect on the immune system. As such, this vaccine is less useful in an outbreak situation.
Resolving the Bundibugyo outbreak
At this time, scientists are working on three candidate vaccines that will need to be developed and studied in clinical trials.
Candidate vaccines
Scientists already know that people gain protection to the virus by making an immune response to a protein that sits on the surface of the virus, so that is the target for vaccination. Currently, three different approaches are being pursued:
- Recombinant VSV vaccine: This approach uses the same design as the existing Zaire Ebola virus vaccine that protects against the Zaire strain, known as Ervebo. This is the vaccine that is approved for use in the U.S. This vaccine strategy delivers the gene for the target protein via a carrier virus that does not cause disease in people, in this case a recombinant version of VSV. The existing vaccine has been used successfully in two outbreaks and in preventive campaigns.
- ChAdOx viral vector vaccine: This vaccine uses the same technology as the Oxford/AstraZeneca COVID-19 vaccine. The gene for the target protein is inserted into a chimp adenovirus that can no longer replicate. When the vaccine is administered, cells make the adenovirus proteins as well as the target protein. This type of vaccine can be manufactured quickly, which offered an advantage during the COVID-19 pandemic and will also be important in this situation. In contrast to the VSV platform, where there are data and experience with the Zaire ebolavirus, no candidate Ebola vaccines have been tested using this platform, so pathogen-specific data are limited.
- mRNA vaccine: Vaccines using mRNA technology were first licensed during the COVID-19 pandemic. Like the viral vector vaccines, mRNA vaccines offer the advantage of short production timelines. These vaccines deliver mRNA for the target protein so that the recipient’s own cells produce the protein against which an immune response is mounted. To see more about how mRNA vaccines work, check this animation. Although this animation is specific for COVID-19 vaccines, the processing and development of immunity works the same way regardless of the specific mRNA delivered.
Getting to approved vaccines
While time is critical in the development of new vaccines, plans for the clinical trials are still being finalized. As of mid-June 2026, we know the following:
- Just as Operation Warp Speed (OWS) worked in the U.S. during the COVID-19 pandemic, funds have been committed to fast-tracking the three candidate vaccines in the hope that at least one will prove safe and effective. Whereas the U.S. government funded the work of OWS, two groups that work internationally have stepped up to support this effort. The Coalition for Epidemic Preparedness (CEPI) has committed at least $60 million to support manufacturing materials, preclinical and phase 1 testing, and simultaneous manufacturing of candidate vaccines. The second group, Gavi (Global Alliance for Vaccines and Immunizations), has made $40 million available to support manufacturers in increasing production capacity. These combined efforts will ensure that if one of the vaccines is demonstrated to be safe and effective, doses can be rapidly deployed.
- Various globally based governmental and scientific partners are working to ensure ethical and safe clinical trials. The World Health Organization (WHO), the governments of the currently impacted countries, the Africa Centres for Disease Control and Prevention (Africa CDC), as well as others are collaborating to ensure that the clinical trials are developed and implemented to assess safety and efficacy while also adhering to ethical standards. Global initiatives such as this follow the WHO R&D Blueprint, aimed at responding to pressing epidemiologic situations and fast-tracking processes to ensure the availability of effective tests, vaccines and medicines. While the processes are designed to move quickly, they still abide by the ethical and scientific principles important in research and development.
- Final trial designs, including which candidate vaccines are tested in phase 3 trials, will depend on early data.
A viable vaccine is still at least months away, which means that in the short term, the primary tools for containment will be those that have historically formed the backbone of public health: contact tracing, isolation, and infection prevention in healthcare settings. In this case, safe burial practices as well as ongoing community engagement and trust building will also determine the effectiveness of current containment efforts and future acceptance of vaccines.