WHO says trial of potential Ebola prevention drug has begun

The World Health Organization said on Tuesday that the first clinical trial is under way of an antiviral drug for people exposed to the Bundibugyo Ebola strain spreading in the Democratic Republic of Congo.

The trial, called EBO-PEP, is assessing whether the antiviral obeldesivir can work as post-exposure prophylaxis for people who have been in contact with confirmed Bundibugyo cases. The experimental drug is taken orally and was developed by the US pharmaceutical company Gilead Sciences. The WHO said it has shown efficacy in pre-clinical models against viruses in the wider filovirus family, which can cause haemorrhagic fevers.

WHO director-general Tedros Adhanom Ghebreyesus confirmed the trial's launch in a post on X. He said that, if effective among high-risk contacts after exposure, the drug could mark a major step forward in preventing contacts from developing disease.

There are no approved vaccines or treatments for Bundibugyo. According to the DRC's latest official figures, the rare Ebola species has infected more than 1,960 people and killed more than 700. The outbreak was declared on May 15 after several deaths in Ituri, a mineral-rich northeastern province affected by armed groups.

Cases have been found in five DRC provinces and in neighbouring Uganda, while more than 90 percent of cases are still being detected in Ituri. Ebola spreads through close contact and infected bodily fluids.

The first patients for the obeldesivir trial are being recruited at PEP centres set up beside Ebola treatment centres run by the NGO The Alliance for International Medical Action, known as ALIMA, in Bunia and Rwampara in Ituri. The trial aims to recruit nearly 1,000 participants aged 12 and over who had direct contact with a confirmed case within the previous five days and are not showing symptoms. Each participant will be monitored daily for 21 days, with a final visit at 42 days.

Earlier on Tuesday, the WHO said the Bundibugyo outbreak in the DRC could be at least two to four times larger than official figures suggest. WHO emergencies chief Chikwe Ihekweazu, speaking after returning from Bunia, said the outbreak continued to outpace response efforts. He said 80 percent of new cases were outside known contact lists and came from unknown chains of transmission, and expressed alarm that many newly reported cases were people who died without reaching a health facility.

A separate trial of two potential treatments for patients with Bundibugyo began in Ituri on July 2. It is evaluating the monoclonal antibody MBP134 and the antiviral drug remdesivir, both alone and in combination. That trial is expected to take months, could run into next year and might need more than 1,000 patients to produce definitive answers.