Ebola cases in DR Congo top 4,000 as WHO recommends Ervebo vaccine trial

The number of confirmed Ebola cases in the Democratic Republic of Congo has surpassed 4,000, according to government figures, as the world's second-largest outbreak shows no signs of slowing.

The DRC Ministry of Health has recorded 4,053 cases of the Bundibugyo virus strain, including 1,850 deaths, since the outbreak was declared in mid-May. The disease has spread to 53 health zones across five provinces: Ituri, North Kivu, South Kivu, Haut-Uele, and Tshopo. Ituri remains the epicenter, accounting for 87% of cases, while neighboring North Kivu accounts for 11%.

This outbreak is described as the fastest-spreading ever recorded, with experts suggesting the true number of cases is likely higher than official statistics. To date, only the 2014-2016 West Africa outbreak was larger, with over 28,000 cases across Guinea, Liberia, and Sierra Leone.

The response faces numerous challenges, including prolonged military conflict, delayed case detection, and shortages of vaccines and treatments. The Ebola virus is transmitted through contact with the bodily fluids of infected individuals.

WHO recommends Ervebo vaccine trial

On March 28, WHO vaccine experts recommended launching a large-scale clinical trial of Ervebo, the only licensed Ebola vaccine, to test its cross-protective capability against the Bundibugyo strain circulating in the DRC, which lacks a specific vaccine.

Ervebo has already proven safe and effective against the more common Zaire strain. WHO experts said preliminary data, particularly from animal trials, suggests the vaccine may also offer some protection against the rare Bundibugyo strain.

In studies, three-quarters of non-human primates vaccinated with Ervebo survived infection with the Bundibugyo strain, compared to a survival rate of only one-quarter in the control group. An unpublished study in ferrets also showed that the research version of Ervebo provided 100% protection against Bundibugyo, while all control animals died within 10 days.

“Members recommend prioritizing Ervebo, the only licensed Ebola vaccine, for a randomized clinical trial in the context of the current outbreak,” a WHO statement said.

However, the WHO's Technical Advisory Group on Candidate Vaccine Prioritization (TAG-CVP) said a vaccine specific to the Bundibugyo strain remains the preferred option for addressing the current outbreak. The group also warned against taking action or conducting trials before sufficient findings are available.

“Expectations should be managed regarding potential protective effects if used in a Phase III ring vaccination trial, as efficacy against symptomatic disease and transmission may not be high, while protection against death may still be achievable,” the report stated.

Currently, two potential vaccines for the Bundibugyo strain are in early-stage human clinical trials, with another being studied for entry into that phase.

The Gavi vaccine alliance maintains a stockpile of 500,000 doses of Ervebo and said it would provide doses from this reserve for the trials, with some already available in the DRC.

“This is already the largest Ebola outbreak in the DRC's history and could become the largest ever recorded,” said Gavi CEO Sania Nishtar. “Given the terrible burden on communities and frontline workers, we are encouraged that the approved Ervebo vaccine could help mitigate severe disease and deaths.”