The Democratic Republic of Congo is distributing 70,000 doses of an Ebola vaccine in an attempt to curb the devastating outbreak . Congo’s outbreak has become the fastest-growing Ebola epidemic ever recorded. More than 5,700 confirmed infections and nearly 2,800 deaths had been reported by August 28. The speed of transmission has raised concerns that the outbreak could eventually surpass the 2014-2016 West African Ebola epidemic, which killed more than 11,000 people.

Ervebo, the vaccine being distributed, was designed for the Zaire Ebolavirus, not the Bundibugyo virus (BDBV) strain which is causing the current outbreak. Experts and the World Health Organization (WHO) have previously been hesitant to use it in this outbreak due to a lack of evidence that it will be effective. However, the increasingly dire situation in DR Congo, combined with new research data has resulted in a change of plan .

“The outbreak continues to expand at a pace that is keeping it on track to becoming one of the deadliest Ebola outbreaks in history," said Dr. Boghuma K Titanji, MD, PhD, physician scientist, infectious diseases physician and assistant professor of medicine at Emory University in Atlanta, GA. "The reasons the WHO has decided to utilize Ervebo are a combination of expanding data to justify its use and the severity of the outbreak, which is not contained at this time."

Fifty thousand doses will be used to vaccinate frontline and healthcare workers, while another 20,000 will be used in a clinical trial designed to collect evidence to determine whether the vaccine can protect against the virus currently spreading through Congo.

Dr. Titanji notes that studies in nonhuman primates suggest that Ervebo, which may also provide some cross-protection against Bundibugyo virus, the cause of the current outbreak. There is also emerging evidence from human studies that people previously vaccinated with Ervebo, as well as those who have recovered from Zaire Ebola virus infection, develop antibodies that can recognize and perhaps provide some protection against Bundibugyo virus.

“Given the pace at which the outbreak is progressing, the calculus here is if we have a tool that can confer at least partial protective benefits it is worth deploying it in the context of a clinical trial while waiting for BDBV Ebola specific vaccines to go through clinical trials and be rolled out,” said Dr. Titanji.

There are a number of vaccines specifically designed to target the Bundibugyo strain in various stages of development. Canada has begun a phase I trial of a mRNA vaccine developed by Moderna, with the first participants dosed in early August . Another vaccine developed in Oxford, U.K., is also already in early human clinical trials , but even if the trials are successful, the vaccines will not be available for people in DR Congo for several months.

“Clinical trials take time. The phase 1 study for the Oxford vaccine is projected to release preliminary results, hopefully by the end of October. After that there will be a phase 2 study and then finally a phase t3 trial if the preceding studies justify the continued study of this candidate vaccine. Realistically we could be looking at 6-9 months before this vaccine enters a phase 3 trial," said Dr. Titanji.

The outbreak is being driven not only by the virus itself but by conditions that make infectious disease control extraordinarily difficult, including armed conflict, population displacement, attacks on healthcare workers and limited healthcare infrastructure.

“While vaccines are an important and valuable tool to help in these types of outbreaks, the core principles of tracing contacts of the confirmed cases and isolating them is what will ultimately stop the chains of transmission. This is underway and improving, but resources are needed to make sure that these efforts catch up to the pace of the outbreak,” said Dr. Titanji.