The Most Promising Ebola Vaccine Has Been Sitting on the Shelf for 15 Years
Efforts to develop a vaccine against the Bundibugyo strain of Ebola have accelerated as the current outbreak reaches a scale and scope comparable to the 2013 to 2016 crisis. Researchers are working to advance a rVSV-based vaccine candidate, which relies on technology similar to the previously established Ervebo vaccine. According to Geisbert, a researcher involved in the study, this candidate is being positioned as a potential tool for ring vaccination, despite significant funding and logistical challenges.
Did You Know? In a 2023 study, researchers found that monkeys were protected from the virus even after exposure when administered the rVSV-based vaccine, a critical factor for the success of ring vaccination strategies.
Why the Bundibugyo Strain Presents Unique Challenges
The development of a vaccine for the Bundibugyo strain has historically faced obstacles due to a lack of perceived financial incentive and the virus’s association with lower mortality rates compared to other strains. According to Courtney Woolsey, an assistant professor at the University of Texas Medical Branch, the limited development since 2023 is largely attributed to these funding barriers and the unexpected nature of the current outbreak. Geisbert notes that if the 2012 outbreak had occurred after the major Zaire outbreak, pharmaceutical companies might have been more inclined to commercialize a vaccine specifically for this strain.
The Path Toward Human Trials
The Coalition for Epidemic Preparedness Innovations (CEPI) has provided up to $3.2 million to facilitate the manufacturing and testing of the vaccine candidate. Rachael Bonawitz, filovirus disease programme lead at CEPI, stated that the extensive safety data and regulatory experience gained from Zaire-strain vaccines could help expedite approval pathways for this new candidate. The International AIDS Vaccine Initiative is currently preparing the candidate for production, marking a transition from laboratory research to potential clinical application.
Expert Insight: The move to leverage existing rVSV platforms represents a strategic attempt to bypass the years of foundational safety testing that typically slow vaccine development. By building on the “Bundibugyo Ervebo” concept, researchers are betting that established manufacturing processes and regulatory precedents will allow them to respond to the current outbreak more rapidly than starting from scratch.
What Happens Next?
While the vaccine candidate shows promise, its ultimate effectiveness remains uncertain due to the inability of scientists to secure a live Bundibugyo virus sample for testing. Stretched resources in the Democratic Republic of the Congo and logistical complexities regarding the transport of refrigerated blood have prevented direct laboratory validation. Although current sequences appear 98-percent similar to past strains, the unknown 2 percent poses a risk that the vaccine may not perform as effectively as previous versions. If the candidate proves successful in clinical material preparation, it could be available for use in future outbreaks, even if it is not deployed in time for the current one.
Frequently Asked Questions
What is the primary barrier to developing this vaccine?
The primary barriers are a lack of financial incentive for manufacturers and the logistical difficulty of obtaining live virus samples from the Democratic Republic of the Congo for testing.
Why is the 2023 monkey study significant?
The study demonstrated that the vaccine could protect monkeys even after they were exposed to the virus, which is a necessary proof of concept for the effectiveness of ring vaccination strategies.
Is the vaccine guaranteed to work against the current strain?
No, because scientists have been unable to test the vaccine against a live sample of the current strain. While sequences are 98-percent similar to previous outbreaks, the remaining 2 percent of unknown genetic material creates a level of uncertainty regarding its efficacy.
How would the availability of a proven vaccine change the way public health officials respond to future Ebola outbreaks?