“We thought it was probably the least likely thing to show up,” says Geisbert. “We were wrong.”
Concerned about this knowledge gap, he decided to modify the vaccine in 2011, leading to research on crab-eating macaques. In the same study, he also finally tested a mixture of existing Ebola vaccines against the Bundibugyo strain, but they did not provide 100 percent protection.
If the 2012 outbreak had followed a larger outbreak in Zaire, Geisbert says, perhaps pharmaceutical companies would have been more interested in commercializing a vaccine that protects against the Bundibugyo strain.
But with the current outbreak nowhere near the scale and scope of the 2013-2016 outbreak, catch-up efforts are becoming increasingly active. Geisbert suspects that the WHO’s experience with Ervebo is one of the reasons they prefer its vaccine candidate, which is basically “Bundibugyo Ervebo,” he says.
WHO also noted the success of a similar rVSV-based vaccine against the Sudanese strain of Ebola in a 2025 ring vaccination trial.
The suitability of the rVSV-based Bundibugyo candidate for ring vaccination was confirmed by a 2023 study that showed that most monkeys were protected from the virus even after exposure when they were vaccinated. This is very important for the effectiveness of ring vaccination. While the researchers vaccinated the monkeys as fast as 20 minutes after infection, the proof-of-concept set it apart from Moderna and the University of Oxford’s candidates in development.
“After that 2023 study, there wasn’t much development because we didn’t expect to see that strain, and because historically it was also associated with a lower death rate,” said Courtney Woolsey, lead author of the paper (Geisbert was a co-author) and an assistant professor at the University of Texas Medical Branch.
“Nobody’s really making money from these vaccines,” she adds, “so there are funding barriers to pushing these vaccines where people probably aren’t going to make money.”
The nonprofit Coalition for Innovation in Epidemic Preparedness has offered up to $3.2 million in funding to develop and begin testing the material needed to make Gesbert’s vaccine, the first step toward human trials.
The “extensive safety data and prior regulatory experience” of the rVSV-based vaccines used to combat the Zaire strain “could help speed up approval pathways if shown to be successful,” Rachel Bonowitz, head of the filovirus disease program at CEPI, told WIRED by email, adding that developers would also be able to build on existing manufacturing processes.
“Even if it’s not used in this outbreak, we hope that there will be clinical material that can be used in humans available for the next outbreak,” Geisbert says, “because it’s likely to come up again.”
While it’s promising, there’s still a chance his vaccine won’t work. Scientists were unable to obtain a live sample of the Bundibugyo virus for testing due to limited resources in the DRC and the logistical and bureaucratic difficulties of obtaining and transporting chilled blood back to the US. Although scientists believe that the current strain is about 98 percent similar to the strain that caused previous outbreaks, that unknown 2 percent poses a risk that the vaccine will not be as effective as against the previous strain.
“If you look at the sequences, they’re not different enough that I can predict there’s going to be a problem, but nothing is certain,” says Heisbert.
The International AIDS Vaccine Initiative in New York will prepare the vaccine candidate for production. The nonprofit biomedical research organization focuses on developing vaccines against global diseases for which there is little financial incentive to develop.
“The baton has been passed and I just sit back and hope it works, whether it’s a vaccine or someone else’s vaccine,” says Geisbert.