Ebola Vaccine Development Remains an Urgent Priority

With the current Ebola outbreak causing a course of despair in West Africa and fueling fears of an epidemic in the United States, efforts to quickly develop a vaccine against virus are under the microscope.

Since several promising Ebola vaccine candidates are currently under various stages of development, the World Health Organization (WHO) convened an emergency meeting last week to evaluate the potential of safe and effective treatments. A panel of experts evaluated 2 specific treatments: an experimental drug co-developed by the National Institutes of Health (NIH) and GlaxoSmithKline (GSK) that recently began human testing, and a vaccine from the Government of Canada licensed for further development to American firm NewLink Genetics Corp.

Both treatments demonstrated 100% efficacy in testing on nonhuman primates.

“Participants in the Geneva meeting stressed that phase 1 trials should be expedited and their results shared broadly in order to facilitate rapid progression to phase 2,” wrote Rupa Kanapathipillai, MD, et al, in a commentary in the New England Journal of Medicine. “If the results in phase 1 are favorable, the consensus was that phase 2a studies should be conducted in Africa, but outside the current Ebola outbreak zone, and should proceed in parallel with phase 2b studies conducted in exposed populations. This approach will provide robust efficacy and safety data as quickly as possible.”

The candidate drug co-developed by the NIH and GSK is based on an attenuated strain of a chimpanzee cold virus, which is used as a carrier to deliver benign genetic material derived from a strain of the Ebola virus. The material contained in the vaccine does not cause an infection; instead, it delivers viral genetic material to human cells without further replication, thus allowing the recipient’s cells to express a protein that generates an immune response.

The phase 1 trials are anticipated to conclude by the end the year, while deployment of the drug could be fast-tracked if the vaccine is determined to be safe and immunogenic, according to the NIH.

The vaccine developed by Canada and NewLink Genetics, called VSV-EBOV, has shown promise in animal testing but has yet to be considered in humans. Canada licensed the rights to American firm BioProtection Systems Corp for further development of the drug for human use.

“The consensus at the Geneva meeting was that there are reasonable alternatives if individually randomized controlled trials are not acceptable in some settings—for example, studies using a stepped-wedge design,” the commentary noted. “A basic principle of every study design should be that all participants will receive Ebola vaccine at some point. There was also agreement that health care workers who care for patients with Ebola or are otherwise exposed to patients' body fluids in hospitals and clinics, family members caring for patients with Ebola at home, and people who cleanse and bury deceased patients should be among those given the opportunity to participate in the early phase 2 trials.”

Other promising therapies in various stages of development include Johnson & Johnson’s drug that is projected to begin clinical testing in early 2015; Tekmira Pharmaceuticals’ RNA interference treatment, called TKM-Ebola; and the highly publicized ZMapp, which reversed Ebola infection in 100% of subjects during animal testing.

Researchers are also evaluating convalescent blood and plasma therapies, which provide an added benefit in strengthening basic public health infrastructures through the development of quality blood services in affected countries.

“Even if adequate safety and immunogenicity are demonstrated in the phase 1 studies, vaccines will not be available in substantial quantity until the first quarter of 2015 at the earliest,” Dr. Kanapathipillai wrote. “For that to occur, funding must be secured for production. Even if an effective vaccine can be produced, it is not likely to be 100% effective, so to succeed in stemming the current outbreak, a coordinated effort to improve capacity and provide clinical care in affected countries needs to be scaled up urgently.”