“We thought that was probably the most likely outcome,” Geisbert said. “We guessed wrong.”
Concerned about that knowledge gap, in 2011 he decided to change the principle, which led to research on macaques that eat crabs. In the same study, he finally tested a combination of ebola vaccines in Bundibugyo, but it did not provide 100 percent protection.
If the 2012 outbreak happened after the big outbreak in Zaire, Geisbert says, pharmaceutical companies may have been more willing to sell a vaccine that protects against the Bundibugyo strain.
But with the current outbreak rivaling those of 2013 to 2016 in scale and scope, efforts to play catch up are in high gear. Geisbert suspects that the knowledge of WHO and Ervebo is one of the reasons why they like the person who will vaccinate, which is “Bundibugyo Ervebo,” he says.
The WHO also noted the success of a similar rVSV-based vaccine targeting the Sudanese strain of ebola in a 2025 ring vaccine trial.
The suitability of the rVSV-based Bundibugyo candidate for ring vaccination was supported by a 2023 study showing that the majority of monkeys were protected from the virus even after being exposed to the vaccine. That is important for ring vaccination to work. While the researchers immunized the monkeys unusually quickly 20 minutes after exposure, the proof of concept set them apart from the Moderna and Oxford University researchers.
“There hasn’t been much progress since that 2023 study, because we didn’t really expect to see that complication again because historically it’s been associated with low mortality,” said Courtney Woolsey, lead author on the paper (Geisbert was a co-author) and assistant professor at the University of Texas Medical Branch.
“No one is really making money with these vaccines,” he adds, “so there are barriers to getting money and moving these vaccines forward where people may not be making money.”
The nonprofit Coalition for Epidemic Preparedness Innovations has awarded up to $3.2 million in funding to develop and begin testing the materials needed to implement Gesbert’s vaccine, which would be the first step toward human testing.
“Extensive safety data and early regulatory information” from the rVSV-based vaccine used to fight the Zaire strain “could help speed up the approval process if it is shown to be effective,” Rachael Bonawitz, who leads the filovirus disease program at CEPI, tells WIRED by email, adding that developers will also be able to build on existing manufacturing processes.
“Even if it’s not used in this outbreak, hopefully there will be clinical material that can be used in humans available in the next outbreak,” Geisbert said, “because it will happen again.”
Although it shows promise, there is still a chance that his vaccine will not work. Scientists were unable to obtain a live Bundibugyo virus sample for testing due to stretched resources in the DRC and operational and bureaucratic difficulties in obtaining and transporting frozen blood back to the US. Although scientists believe that the current strain is about 98 percent identical to the strain that caused the previous outbreak, that unknown 2 percent risks that the vaccine will not be as effective as it was compared to the previous strain.
“If you look at the sequence it’s not different enough that I can predict there’s going to be a problem, but it’s nothing out of the ordinary,” Geisbert said.
The International AIDS Vaccine Initiative in New York will prepare a vaccine candidate for production. A non-profit biomedical research organization focused on developing vaccines for global diseases where there is little financial benefit to development.
“The stick has been given, and I just sit back and hope that it works, whether it’s a vaccine, whether it’s someone else’s vaccine,” said Geisbert.
