Global health authorities are racing to identify medical options to help contain an Ebola outbreak in eastern Democratic Republic of Congo, linked to the Bundibugyo strain of the virus.
Unlike for the more common Zaire strain, there are no approved vaccines or treatments for Bundibugyo.
The latest outbreak has led to about 363 confirmed cases in the Democratic Republic of Congo, including 62 deaths. Bundibugyo ebolavirus, or BDBV, has a fatality rate of up to 40%.
A small number of experimental vaccines and therapies are being assessed, and global health authorities are examining whether any existing Ebola treatments might offer protection, so far supported only by limited animal data.
Most experimental treatments have not yet been tested in humans and would require emergency or compassionate-use authorisation before they are deployed in Congo.
The World Health Organization has recommended prioritising several experimental drugs, including antibodies, antivirals and vaccines, for the treatment and prevention of BDBV.
Here is what we know of these candidates so far:
Vaccines
The WHO said last month a single-dose rVSV Bundibugyo vaccine being developed by the International AIDS Vaccine Initiative is the most promising candidate to prevent BDBV.
The vaccine, rVSVΔG/BDBV-GP, which uses the same technology as Merck’s approved shot Ervebo for the Zaire strain, has shown survival benefit in non-human primates in a 2023 proof-of-concept study.
The WHO said the vaccine’s development would likely take seven to nine months before it is ready for assessment in a clinical trial.
The International AIDS Vaccine Initiative said it is advancing the candidate toward a clinical trial and preparing for manufacturing, including transferring the vaccine virus and processes for good manufacturing practices production.
The global partnership, Coalition for Epidemic Preparedness Innovations, or CEPI, has committed to an initial funding of $3.2 million to advance the vaccine candidate.
The WHO has recommended prioritizing another vaccine candidate, ChAdOx1 Bundibugyo, being developed by Oxford University and the Serum Institute of India.
The potential vaccine is based on ChAdOx1 technology, which was used in the Oxford/AstraZeneca COVID-19 vaccine, and is being manufactured by the Serum Institute.
The company started production under its “emergency response framework,” alongside partners CEPI and the University of Oxford, as soon as it got word of the outbreak this month, a spokesperson said.
CEPI said it would initially invest up to $8.6 million for the development of the shot.
Doses could be ready within two to three months for efficacy assessment through a clinical trial, the WHO said, adding that additional animal studies have yet to be conducted.
The WHO said experts considered a single dose of the vaccine candidate potentially suitable for contacts of Ebola cases, while a two-dose regimen might be used for high-risk but unexposed groups, including healthcare workers and frontline responders.
The Oxford Vaccine Group said it is working to generate pre-clinical data to support the development and testing of the ChAdOx1 BDBV vaccine.
Moderna said it has partnered with CEPI to advance its mRNA-based BDBV vaccine candidate into pre-clinical and early clinical testing. CEPI has committed up to $50 million to support development, including manufacturing, and progression to later-stage trials if early safety and immunogenicity data are positive.
Antibody-based therapies
The WHO has recommended prioritizing privately held Mapp Biopharmaceutical’s pan-ebolavirus antibody drug, MBP134 — a combination of two human monoclonal antibodies — for clinical trials among confirmed BDBV cases.
Initially studied for the Sudan ebolavirus strain, the drug was found to be safe and well tolerated in early-stage trials. Development has been backed by the U.S. Biomedical Advanced Research and Development Authority, or BARDA.
BARDA said it is coordinating shipments of the investigational treatment for potential use in high-risk Americans exposed to the virus.
Mapp said MBP134 has shown similar activity against all known ebolaviruses and that it is working with the WHO and other authorities as part of the response to the Congo outbreak.
Regeneron Pharmaceuticals’ antibody drug candidate, maftivimab, is also being explored as a potential treatment by the WHO. According to the company, it has been shown in a lab to be active against the Bundibugyo ebolavirus.
Regeneron said it is working to prepare existing supply of maftivimab for use in upcoming clinical trials.
The FDA has approved a combination of maftivimab and two other antibodies, atoltivimab and odesivimab, under the brand name Inmazeb, to treat Zaire ebolavirus infection in adult and paediatric patients.
The company said it recently donated 500 doses of Inmazeb to the WHO, which could be used if found helpful.
“Supply of Inmazeb is already on the ground in the DRC, should WHO wish to utilize it for immediate treatment or as an additional component of the study,” Regeneron said.
Human monoclonal antibodies isolated from Bundibugyo survivors have also been explored as potential treatments.
One candidate, BDBV289-N, demonstrated efficacy in a 2018 animal study. The study, conducted by a group of researchers with support from the U.S. National Institutes of Health, showed the antibody gave up to 100% protection in infected monkeys, even when treatment started up to eight days after the infection.
Antiviral drugs
Gilead Sciences’ experimental oral antiviral drug obeldesivir is being considered as a potential post-exposure treatment by the WHO to prevent those exposed to Ebola from developing the disease.
Once-daily obeldesivir given for 10 days provided up to 100% protection in monkeys against the Zaire and Sudan Ebola strains when treatment began 24 hours after exposure.
“Obeldesivir is predicted to be active against this particular (Bundibugyo) strain. While not approved for this, we do have preclinical data that shows positive results,” a company spokesperson said.
Gilead’s antiviral remdesivir has shown activity against the Bundibugyo virus in laboratory studies conducted by researchers at the University of Texas Medical Branch. Some data suggest the drug, given as an intravenous infusion, may have stronger activity against BDBV than against the Zaire Ebola strain.
The WHO has also recommended a combination therapy using a monoclonal antibody and remdesivir for evaluation.
Diagnostic tests
The WHO had indicated that limited testing capacity for the Bundibugyo strain was slowing response to the outbreak. Here are tests that can detect the infection :
Roche said it has developed a research-use-only molecular polymerase chain reaction test to detect Ebola Bundibugyo virus. The test was developed by TIB MOLBIOL, a Roche unit.
The drugmaker said it is working with public health laboratories and authorities to make the test available in the affected regions.
BioFire Defense, an affiliate of French diagnostic firm bioMerieux, makes an FDA-cleared test – BioFire Global Fever Special Pathogens Panel – that can detect multiple Ebola species, including Bundibugyo.
A company spokesperson said it is increasing production capacity and engaging with public health stakeholders and international contacts to assess potential needs.
Germany-based firm Altona Diagnostics’ test, called RealStar Filovirus Screen RT-PCR Kit 1.0, is being used to detect the Bundibugyo outbreak in Congo. The firm has ramped up production to support local testing facilities in Congo.