WHO launches first trial of antiviral to prevent Bundibugyo strain of Ebola

The World Health Organization (WHO) announced on Tuesday the launch of the first clinical trial to test the effectiveness of an antiviral drug in people exposed to the deadly Bundibugyo strain of Ebola, which is spreading in the Democratic Republic of Congo (DRC).

The trial, named EBO-PEP, will assess the ability of the antiviral obeldesivir to prevent disease in individuals who have had contact with confirmed Bundibugyo cases. The experimental drug, developed by US pharmaceutical company Gilead Sciences, is administered orally and has shown efficacy in pre-clinical models against viruses in the wider filovirus family that cause hemorrhagic fevers. Clinical trials represent the stage where a promising drug is tested in humans.

WHO Director-General Tedros Adhanom Ghebreyesus confirmed the trial's launch in a post on X. "Every breakthrough begins with hope," he wrote. "If effective among high-risk contacts after exposure, this could mark a major step forward" in preventing contacts from developing disease, he added.

There are currently no approved vaccines or treatments for Bundibugyo. According to the DRC's latest official figures, this 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 north-eastern province plagued by armed groups. Ebola, which spreads through close contact and infected bodily fluids, has been found in five DRC provinces and in neighboring Uganda. However, more than 90% of cases are still being detected in Ituri.

First patients for the obeldesivir trial are being recruited at Post-Exposure Prophylaxis centers set up adjacent to Ebola treatment centers operated by the NGO ALIMA in Bunia and Rwampara, Ituri. The trial aims to recruit nearly 1,000 participants aged 12 and over who have had direct contact with a confirmed case within the preceding five days but are not showing symptoms. Each participant will be monitored daily for 21 days, with a final visit at 42 days.

On Tuesday, the WHO said the true scale of the Bundibugyo outbreak in the DRC could be two to four times larger than official figures suggest. Returning from Bunia, WHO emergencies chief Chikwe Ihekweazu told reporters in Geneva that the outbreak "continues to outpace the response efforts." He said 80% of new cases were outside the lists of known contacts and were "from unknown chains of transmission," and voiced alarm that many newly reported cases were people who died without ever reaching a health facility.

The 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, alone and in combination. The trial will take months and could even run into next year, and might require more than 1,000 patients to produce definitive answers.