WHO launches EBO-PEP trial to test Obeldesivir for preventing Bundibugyo Ebola outbreak

DRC—With no approved vaccine or specific treatment available for the ongoing Bundibugyo Ebola virus disease outbreak, the WHO and its partners have launched a major clinical trial to evaluate potential post-exposure preventive therapies.

The initiative prioritizes obeldesivir, an experimental oral antiviral developed by Gilead Sciences, as a post-exposure prophylaxis (PEP) candidate for people at high risk of infection.

Laboratory studies have shown that the drug is active against several filoviruses, including the Bundibugyo Ebola virus, prompting experts to assess its effectiveness during the current outbreak.

According to the DRC’s National Institute of Public Health (INSP), the outbreak in the Democratic Republic of the Congo (DRC) and Uganda had infected 1,759 people and claimed 600 lives as of 9 July 2026.

EBO-PEP trial begins participant recruitment

The EBO-PEP platform trial, which has been under development since 2024, will evaluate several medicines as post-exposure prophylaxis for people who have had high-risk contact with filoviruses, the virus family that includes Bundibugyo Ebola.

The programme will eventually operate across the DRC, Uganda, Guinea, Liberia and Sierra Leone.

Its first study protocol focuses on testing obeldesivir as a preventive treatment for high-risk contacts in the DRC and Uganda.

Researchers began recruiting participants on 14 July 2026 in Ituri Province, the epicentre of the outbreak in the DRC.

Humanitarian organisations ALIMA (The Alliance for International Medical Action) and Médecins Sans Frontières (MSF) will support field operations.

Recruitment will take place at PEP centres established next to ALIMA-operated Ebola treatment units in Bunia and Rwampara.

The trial aims to enrol nearly 1,000 participants, although the final number will depend on how the outbreak evolves.

Eligible participants include adults and children aged 12 years and older who have had direct contact with a confirmed Ebola case within the previous five days.

Eligible exposures include contact with an infected patient, an Ebola-related corpse, or a contaminated needle. Participants must not show symptoms of Ebola at enrolment.

Researchers will monitor each participant daily for 21 days, followed by a final assessment on day 42.

Second study to evaluate remdesivir for vulnerable groups

A second EBO-PEP protocol will assess remdesivir under compassionate use for children younger than 12 years and pregnant or breastfeeding women who have experienced high-risk exposure.

Researchers selected remdesivir for these groups because available safety and efficacy data on obeldesivir remain insufficient to support its use in these populations.

International collaboration drives the trial

ALIMA coordinates the EBO-PEP trial alongside a broad network of national and international partners.

The trial’s principal investigators are Professor Pauline Byakika-Kibwika of Mbarara University of Science and Technology (MUST) in Uganda, Dr Marie Jaspard of Saint-Antoine Hospital/Inserm in France, and Professor Placide Mbala of the National Institute for Biomedical Research (INRB) in the DRC.

The INRB and ANRS Emerging Infectious Diseases (ANRS MIE), an autonomous agency of the French National Institute of Health and Medical Research (Inserm), are conducting the study.

Africa CDC and international partners provide financial support

The Global Health EDCTP3 Partnership, supported by the European Commission, has awarded EUR 3.4 million (US$3.99 million) to launch the project.

Meanwhile, the Africa CDC has committed US$1 million in direct funding.

The organisation also helped secure an additional US$2 million from South Africa and US$3 million from the DRC during a high-level meeting held in Kinshasa on 2 July 2026

This meeting brought together DRC President Félix Tshisekedi and South African President Cyril Ramaphosa, who serves as the African Union Champion for Pandemic Prevention, Preparedness and Response.

Beyond financial support, Africa CDC is contributing scientific leadership through Dr Mosoka P. Fallah, who is working alongside Professor Placide Mbala to coordinate the study.

The agency is also providing technical assistance to field teams in Bunia, including trial simulations and the identification of high-risk contacts.

Experts highlight the importance of post-exposure prevention

WHO Director-General Dr Tedros Adhanom Ghebreyesus said preventing infection among exposed individuals is essential for containing the outbreak.

He noted that, if successful, EBO-PEP could establish post-exposure prophylaxis as an important new strategy for preventing Ebola among people exposed to the virus while complementing contact tracing and community engagement efforts.

Africa CDC Director-General Dr Jean Kaseya described Ebola exposure as a frightening experience for healthcare workers, families and communities.

He said the trial offers an opportunity to intervene before infection develops into disease and urged partners to close the remaining funding gap while preparing for equitable access should obeldesivir prove safe and effective.

Professor Placide Mbala, a virologist at the INRB and co-principal investigator, said the project originated from field observations suggesting that medicines used to treat filovirus infections might also prevent disease among exposed family members and healthcare workers.

Co-principal investigator Dr Marie Jaspard, an infectious disease specialist at Saint-Antoine Hospital and Inserm researcher, said the trial seeks to determine whether antiviral treatment can prevent infection among people with close exposure to the Bundibugyo Ebola virus.

She added that positive findings could help reduce transmission during future outbreaks.

Professor Pauline Byakika-Kibwika said that, in the absence of a vaccine against the Bundibugyo Ebola virus, protecting exposed individuals, particularly healthcare workers, is critical to interrupting transmission.

She noted that the study aims to generate evidence supporting post-exposure prophylaxis while strengthening preparedness for future outbreaks.

Professor Yazdan Yazdanpanah, Director of ANRS MIE and co-sponsor of the trial, said the study addresses a major gap in filovirus outbreak response by evaluating post-exposure prevention alongside vaccines and therapeutic treatments.

Dr Moumouni Kinda, Director-General of ALIMA, said the project demonstrates the value of integrating clinical research with humanitarian response.

He added that ALIMA remains committed to coordinating and implementing the trial under challenging field conditions while supporting efforts to localise research capacity in Africa.

Building research capacity across Africa

In addition to evaluating new prevention strategies, EBO-PEP aims to strengthen African researchers’ capacity to conduct clinical trials.

Preparatory activities completed in 2025 enabled organisers to deliver an intensive training programme in Bunia, Ituri Province, from 30 June to 4 July 2026.

The course covered drug safety, clinical trial data management, patient care, clinical monitoring, and the collection, processing and management of biological samples.

The project also seeks to promote broader adoption of post-exposure prophylaxis by helping improve access to effective medicines if the strategy proves successful.