20 April 2026 Articles

Last study participant followed up in large-scale Ebola booster vaccination study in Mbandaka

A major milestone in the EBO-BOOST clinical trial brings us closer to more effective Ebola vaccination strategies and improved local outbreak preparedness.

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On Friday 17 April, the final participant in the EBO-BOOST clinical trial attended a routine follow-up visit at the Laboratoire provincial de santé publique et recherche in Mbandaka, the capital of Equateur Province in the Democratic Republic of the Congo (DRC). This moment marks an important milestone in the search for the optimal combination of Ebola booster vaccines and long-lasting immune protection against the virus.

Study participants waiting outside the Provincial Laboratory of Mbandaka.

Towards flexible Ebola vaccination strategies

EBO-BOOST is a clinical trial investigating how Ebola booster vaccines can best be deployed. Although two vaccines are currently approved, it remains unclear how long protection lasts and what the optimal revaccination strategy is. The study compares different combinations in people who were previously vaccinated and examines whether combining different vaccines ("mix-and-match") is as safe and effective as repeating the same vaccine. Through this project, researchers aim to accelerate vaccine deployment during outbreaks, develop clear revaccination guidelines, and strengthen local epidemic preparedness.

"With this trial, we want to create more flexibility in vaccination strategies," says Prof Wim Adriaensen, Head of the Clinical Immunology Unit at ITM and principal investigator of the study. "If different vaccines prove to be interchangeable, we can respond more quickly and efficiently to outbreaks, depending on local conditions and vaccine availability."

Blood sampling

Ebola remains a threat

The Ebola virus continues to pose a serious threat in Central and West Africa, particularly in the DRC. The disease causes severe symptoms such as high fever, vomiting, and internal bleeding, and has a high mortality rate.

Since the discovery of the virus in 1976, multiple outbreaks have occurred, especially in countries in Central and West Africa, including the DRC. Mbandaka, the capital of Equateur Province with more than one million inhabitants, has experienced several epidemics in recent years, including as recently as 2022. Thanks to international efforts, vaccines have been developed that offer protection, but the duration of that protection is not yet fully understood. The EBO-BOOST project aims to address this gap.

In the lab

Final study participant followed up

The last group of study participants visited the provincial laboratory in Mbandaka during the week of 13 April for a routine check-up, blood sampling, and an oral swab, six months after receiving the booster vaccine. For the study, participants were recruited who had received an Ebola vaccine one to five years earlier during previous outbreaks. Based on the measured levels of antibodies in the blood, researchers are studying the immune response. This will help them better understand how long protection lasts and which booster strategy is most effective. In total, 624 study participants were followed at different time points after their initial booster vaccination.

Researchers are currently assessing whether extending the study could provide additional insights. If so, participants may also be followed up again after 12 and 24 months to measure the immune response over a longer period.

Saïdou Milua et Lucien Boba, lab technicians at INRB, carry the samples to the Programme Elargi de Vaccination (PEV) for storage. Afterwards, they will be shipped to the lab in Kinshasa for analysis.

Next steps

In the coming months, the collected data will be further analysed in the laboratory of INRB in Kinshasa.

The impact of EBO-BOOST goes beyond the study results alone. Thanks to investments in local research infrastructure, complex immunological analyses can now be conducted within the DRC, without the need to send samples abroad. This strengthens preparedness for future epidemics—not only Ebola, but also other infectious diseases.

The study is a strong collaboration with the Institut National de Recherche Biomédicale (INRB), a long-standing ITM partner. It is funded by the Coalition for Epidemic Preparedness Innovations (CEPI), Merck Sharp & Dohme (MSD), and the Directorate-General for Development Cooperation and Humanitarian Aid (DGD).

EBO-BOOST study team with partners from ITM and INRB in front of the Provincial Lab of Mbandaka.

EBO-BOOST

We aim to address the ongoing threat of the Ebola Virus Disease by investigating optimal timing and safety of booster vaccinations for rapid deployment during outbreaks, and strengthening local epidemic preparedness.

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