The results of a small trial of an experimental Ebola vaccine in humans shows that it appears safe, produces an immune response and is well tolerated, prompting support for its development to be fast-tracked.

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The first participant, a 39-year-old woman, receives a dose of the experimental Ebola vaccine at the NIH Clinical Center.
Image credit: NIAID

The candidate vaccine is being jointly developed by the National Institute of Allergy and Infectious Diseases (NIAID) – one of the National Institutes of Health (NIH) – and the global health care company GlaxoSmithKline (GSK).

A preliminary report on the VRC 207 trial, which tested the safety of the vaccine in 20 healthy adults at the NIH Clinical Center in Bethesda, MD, is published in the New England Journal of Medicine.

The unprecedented scale of the current Ebola epidemic in West Africa has prompted intense efforts to develop safe and effective vaccines, not only to help stem the current spread, but also to prevent future outbreaks.

The vaccine comprises a harmless “carrier virus” – which causes a common cold in chimpanzees and does not cause illness in humans – and genetic material from two strains of Ebola virus: the Sudan strain and the Zaire strain.

The vaccine does not contain Ebola virus and cannot cause Ebola disease, say the developers.

In total, 20 healthy people aged 18-50 volunteered for the trial. Of these, 10 people received a low dose, and 10 received a high dose of the vaccine via intramuscular injection.

The researchers tested the participants’ blood 2 weeks and 4 weeks later to find out whether the vaccine had caused their immune systems to produce antibodies to Ebola.

The results showed that all the participants had produced anti-Ebola antibodies at the 4-week point. The highest levels of antibodies were found in the volunteers who received the higher dose of vaccine.

The results also showed presence of CD8 T-cells in the blood of two volunteers in the low-dose group and seven in the high-dose group. These cells are produced by the immune system and may be an important part of immune protection against Ebola, note the researchers.

Lead investigator Julie E. Ledgerwood, a researcher at the NIAID Vaccine Research Center, explains:

We know from previous studies in non-human primates that CD8 T-cells played a crucial role in protecting animals that had been vaccinated with this NIAID/GSK vaccine and then exposed to otherwise lethal amounts of Ebola virus.

The size and quality of the CD8 T-cell response we saw in this trial are similar to that observed in non-human primates vaccinated with the candidate vaccine.”

The researchers observed no serious adverse effects of the vaccine in any of the volunteers, although two who had the higher dose did have a short fever the day after receiving the injection.

While the trial results are positive and promising, there are still many questions to answer before the vaccine can be considered effective. Part of the problem is that it is not clear what constitutes an effective level of immunity.

Other trials are taking place that may answer some of the unresolved questions, says Daniel D. Bausch, an associate professor at Tulane University School of Public Health and Tropical Medicine, in an editorial accompanying the trial report. He adds:

“The road is still long and there are many challenges, but we are nevertheless one step closer to a solution.”

Prof. Bausch says while there is room for cautious optimism as the Ebola epidemic apparently slows down in some parts of West Africa, there are still pockets of intense transmission, and reports show the outbreak is now spreading into Mali.

These events “remind us that the battle for control is still on. This is no time to be complacent,” he urges.

Medical News Today recently reported on a study of an experimental Ebola vaccine that can be taken in inhaled form that is showing promise in animal trials.