Bundibugyo Ebola vaccine candidate waits 15 years for testing

Bundibugyo Ebola – A Bundibugyo-focused Ebola vaccine built from an older approach has been in limbo for 15 years, but a new round of urgency is pushing it toward preparation for production and potential human trials—while scientists still face a stubborn question: whether today

It was supposed to be the easiest answer, the kind that would show up cleanly in a lab and then move straight into the real world. But when Geisbert and his team tried to model what would work best, they underestimated how unpredictable the virus would be.

“We thought that’s probably the one that’s least likely to pop up,” Geisbert says. “We guessed wrong.”

The gap mattered. In 2011, Geisbert decided to modify a vaccine—an effort that eventually led to a study using crab-eating macaques. In that same study, he also tested a blend of existing Ebola vaccines on the Bundibugyo strain. It did not provide 100-percent protection.

That was the moment the project started to feel like it was waiting for a door to open. Geisbert says that if the 2012 outbreak had occurred after the major Zaire outbreak. pharmaceutical companies might have been more motivated to commercialize a vaccine protecting against the Bundibugyo strain. Instead, time passed—and the candidate remained largely on the shelf.

Now, with the present outbreak rivaling the 2013 to 2016 one in scale and scope, the work of catching up is accelerating. Geisbert suspects WHO’s experience with Ervebo is one reason the agency favors his vaccine candidate, which he describes as “Bundibugyo Ervebo.”

WHO has also pointed to the success of a similar rVSV-based vaccine targeting the Sudan strain of Ebola, tested in a ring vaccination trial in 2025.

For Geisbert’s Bundibugyo rVSV-based approach, that ring-vaccination idea isn’t just a theory. A 2023 study found that most monkeys were protected from the virus even after they were exposed—so long as they had been vaccinated. The researchers vaccinated the monkeys an unrealistically quick 20 minutes after exposure. but the basic proof of concept is what matters for a strategy that depends on rapid response.

That sets the candidate apart from other efforts under development, including those by Moderna and the University of Oxford.

“There hasn’t really been much development since that 2023 study. because we weren’t really expecting to see that strain and also because historically it’s been associated with lower-rate mortality as well. ” said Courtney Woolsey. the lead author on the paper (Geisbert was a coauthor) and an assistant professor within the University of Texas Medical Branch.

Woolsey also points to the reality that rarely stays confined to spreadsheets. “Nobody really makes money off these vaccines,” she adds. “so there are funding barriers as well to advance these vaccines where people likely aren’t going to make money.”

CEPI—an organization that backs epidemic response when markets don’t—has stepped in with money for the next phase. The nonprofit Coalition for Epidemic Preparedness Innovations has offered funding of up to $3.2 million to prepare and start testing the material needed to manufacture Geisbert’s vaccine. It’s the first step toward human trials.

CEPI’s Rachael Bonawitz. filovirus disease programme lead at CEPI. says the “extensive safety data and prior regulatory experience” from rVSV-based vaccines used against the Zaire strain “could help expedite approval pathways if it is shown to be successful.” She adds that developers would also be able to build on existing manufacturing processes.

Still, the candidate’s progress doesn’t erase the central uncertainty that keeps every vaccine effort honest. Even if it looks promising, there is a real chance it won’t work.

Scientists have not been able to obtain a live Bundibugyo virus sample for testing because resources in the DRC are stretched, and because getting and transporting refrigerated blood back to the US involves both logistical and bureaucratic complexity.

Researchers believe the current strain is around 98-percent similar to the strain that caused the previous outbreaks. That “around” is doing heavy lifting. Geisbert says the unknown 2 percent creates risk—because a vaccine tuned to one version may not perform the same way if the virus has shifted.

“When you look at the sequences it’s not different enough that I would predict that there would be a problem, but nothing’s foolproof,” Geisbert says.

Behind the scenes, the effort to turn a lab candidate into something that can be produced is already moving. The International AIDS Vaccine Initiative in New York will prepare the vaccine candidate for production. The nonprofit biomedical research organization focuses on developing vaccines for global diseases where there is little financial incentive for development.

For Geisbert, the handoff is partly a relief—and partly a kind of helpless waiting.

“The baton has been handed off, and I just sit back and hope that it works, whether it’s the vaccine, whether it’s somebody else’s vaccine,” he says.

Ebola vaccine Bundibugyo rVSV CEPI Ervebo WHO ring vaccination International AIDS Vaccine Initiative macaque study Courtney Woolsey Rachael Bonawitz