“We thought maybe this was the one that was least likely to come up,” Geisbert says. “We guessed wrong.”
Concerned by that knowledge gap, in 2011 they decided to modify a vaccine, leading to a study in crab-eating macaques. In the same study, they also eventually tested a mixture of existing Ebola vaccines on the Bundibugyo strain, but they did not provide 100 percent protection.
If the 2012 outbreak had occurred after the major Zaire outbreak, Geisbert says, it’s possible that pharmaceutical companies would have been more eager to commercialize a vaccine that protects against the Bundibugyo strain.
But with the current outbreak rivaling that of 2013 to 2016 in terms of scale and scope, efforts to play catch-up are going into high gear. Geisbert suspects that WHO’s experience with Erwebo is one of the reasons they favor its vaccine candidate, which is basically “Bundibugyo Erwebo,” he says.
WHO also noted the success of a similar rVSV-based vaccine targeting the Sudan strain of Ebola in a ring vaccination trial in 2025.
The suitability of the rVSV-based Bundibugyo candidate for ring vaccination was supported by a 2023 study that showed that most monkeys were still protected from the virus after vaccination. This is important for the ring vaccination to work. While the researchers gave the monkeys an unrealistically quick vaccine, 20 minutes after exposure, the proof of concept sets it apart from candidates under development at Moderna and the University of Oxford.
“There really hasn’t been a lot of development since that 2023 study, because we really weren’t expecting to see that strain and also because historically it’s also been associated with lower-rate mortality,” said Courtney Woolsey, lead author of the paper (Gisbert was a co-author) and assistant professor at the University of Texas Medical Branch.
“Nobody really makes money with these vaccines,” she adds, “so there are also funding hurdles to moving these vaccines forward where people probably won’t be able to make money.”
The nonprofit Coalition for Epidemic Preparedness Innovations has offered up to $3.2 million in funding to prepare the materials needed to manufacture Gesbert’s vaccine and begin testing, which would be the first step toward human trials.
Rachel Bonawitz, head of the filovirus disease program at CEPI, told WIRED over email that “extensive safety data and prior regulatory experience” from the rVSV-based vaccines used to combat the Zaire strain could help accelerate approval pathways.
“Even if it’s not used in this outbreak, hopefully there will be diagnostic material available that can be used in humans for the next outbreak,” Geisbert says, “because this will likely come up again.”
Even though it shows promise, there’s still a possibility that his vaccine won’t work. Scientists have not been able to obtain live Bundibugyo virus samples for testing due to a lack of resources in the DRC and the logistical and bureaucratic complexity of repatriating and transporting refrigerated blood to the United States. While scientists believe the current strain is about 98 percent identical to the strain that caused the previous outbreak, the unknown 2 percent presents a risk that the vaccine will not be as effective as it was against the previous strain.
“When you look at the sequences it’s not different enough that I could predict there would be a problem, but nothing is foolproof,” says Geisbert.
The International AIDS Vaccine Initiative in New York will prepare the vaccine candidate for production. The non-profit biomedical research organization focuses on developing vaccines for global diseases where there is little financial incentive for development.
“The baton has been handed over, and I just sit back and hope it works, whether it’s the vaccine, whether it’s someone else’s vaccine,” Geisbert says.
