The promising Ebola vaccine has been on shelves for 15 years

“We thought this was the least likely option to come up,” says Gisbert. “We guessed wrong.”

Concerned by this knowledge gap, in 2011 he decided to modify the vaccine, which led to a study of crab-eating macaques. In the same study, he also finally tested a combination of existing Ebola vaccines on the Bundibugyo strain, but it did not provide 100% protection.

If the 2012 outbreak had occurred after a large outbreak in Zaire, pharmaceutical companies likely would have been more eager to market a vaccine that protected against the Bundibugyo strain, Gisbert says.

But with the current outbreak rivaling the 2013-2016 outbreak in size and scope, efforts to catch up are well under way. Gaisbert believes the WHO’s experience with Ervebo is one of the reasons they favor his vaccine candidate, which is essentially Bundibugyo Ervebo, he says.

The World Health Organization also noted the success of a similar rVSV-based vaccine targeting the Sudanese Ebola strain 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 protected from the virus even after exposure if vaccinated. This is crucial for the ring vaccination to work. While the researchers vaccinated monkeys unrealistically quickly after 20 minutes of exposure, the proof of concept sets it apart from the Moderna and Oxford University candidates in development.

“There hasn’t really been a lot of development since the 2023 study, both because we didn’t really expect to see this strain and also because it’s been historically associated with lower mortality as well,” said Courtney Woolsey, the paper’s lead author (Gisbert was a co-author) and an assistant professor at the University of Texas Medical Branch.

“No one is really making money from these vaccines, so there are also funding barriers to developing these vaccines, as people probably won’t be able to make money,” she adds.

The nonprofit Coalition for Epidemic Preparedness Innovations has offered up to $3.2 million in funding to prepare and begin testing the materials needed to manufacture the Gisbert vaccine, which would be the first step toward human trials.

“Extensive safety data and prior regulatory experience” from the rVSV-based vaccines used to combat the Zaire strain “could help accelerate approval pathways if they prove successful,” Rachel Bonawitz, head of the Filovirus Diseases Program at CEPI, tells WIRED by email, adding that developers will also be able to build on existing manufacturing processes.

“Even if it is not used in this outbreak, we hope that there will be clinical materials that can be used in humans available for the next outbreak, because it will likely appear again,” says Gisbert.

Although it looks promising, there is still a chance that his vaccine will not work. Scientists have been unable to obtain a live sample of the Bundibugyo virus for testing due to a lack of resources in the Democratic Republic of the Congo and the logistical and bureaucratic complexity of obtaining refrigerated blood and transporting it to the United States. While scientists believe the current strain is about 98% similar to the strain that caused the previous outbreak, the unknown 2% represents 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 would expect a problem, but nothing is guaranteed,” says Gisbert.

The International AIDS Vaccine Initiative in New York will work on preparing 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 down, and I’m sitting back and hoping it works, whether it’s the vaccine, or someone else’s vaccine,” Gisbert says.