Ebola without a vaccine: why the Bundibugyo fever outbreak in the DRC has not been stopped after 50 years

An outbreak no one was prepared for

Fifty years after the first scientifically documented Ebola epidemic of 1976 near the Ebola River in what was then Zaire, the Democratic Republic of the Congo has once again found itself at the center of a major outbreak. This time the pathogen is the less common Bundibugyo virus of the Orthoebolavirus genus, first identified in 2007 during an outbreak in Bundibugyo, Uganda, and detected again in the DRC in 2012. Since May, more than 10,000 cases have been registered in the DRC, and the disease has also been found in Kenya and Nigeria. Deutsche Welle reports on this.

Why there is no vaccine against Bundibugyo

Tropical medicine specialist Torsten Feldt of Düsseldorf University Hospital called the situation a missed opportunity: the virus was known from two previous outbreaks, and, in his words, there was enough time to develop vaccines and treatments, but the chance was not taken, which means time has already been lost during the current outbreak. Leonie Mayer of the German Center for Infection Research (DZIF) agrees that a vaccine and preclinical trials could have been prepared in advance, but stresses that efficacy can only be assessed and confirmed during an actual outbreak.

The problem of different strains and a less aggressive virus

Ebola is not a single virus. The known dangerous orthoebolaviruses include the Ebola virus (formerly Zaire), the Sudan virus, and the Bundibugyo virus. The existing vaccine Ervebo was developed and licensed against the Zaire variant, so for the areas of the current outbreak it is of only limited relevance. Mayer notes that vaccines cannot be developed in advance against every potential pathogen — funding shortages and prioritization take their toll: many researchers considered a new Sudan virus outbreak more likely, and vaccine development against it has progressed further.

What the new study showed

Mayer is the lead author of a recently published studythat examined whether the already licensed Ervebo vaccine can trigger an immune response against other Ebola types. The DZIF team found cross-reactive T-cell responses against the Bundibugyo virus and, to a lesser extent, against the Sudan virus. “We now know that immune cells can most likely also recognize the Bundibugyo virus,” Mayer said, but she emphasized that the data cannot answer whether this immune response provides real protection or merely a milder course of the disease. This, she said, is an important gap in knowledge.

Why Ervebo is not being used on a mass scale

Mayer explains the dilemma: using a vaccine without knowing whether it works is unethical, and once it is used on a mass scale it will no longer be possible to establish its efficacy — a drop in case numbers could be attributed to other measures or to the epidemic having passed its peak. Tropical medicine specialist Jürgen May of the Bernhard Nocht Institute warns that mass vaccination without proven efficacy could create a false sense of security, undermine trust, and make a study impossible. In the worst case, Mayer notes, people might then refuse more effective vaccines.

Diagnostics versus speed of response

Containing the outbreak is hampered not only by medical limitations: conflicts, hard-to-reach transport routes, attacks on medical facilities, and gaps in contact tracing. Feldt notes that detecting Bundibugyo is no longer a problem — the limiting factor is more often the practical availability of diagnostics: in remote or conflict-affected regions, samples have to be transported over long distances. The authors of an article in the latest issue of Nature come to a similar conclusion: the problem is often not detecting cases but the speed of the response — finding Ebola is now easier than stopping it.