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An experimental vaccine to prevent Ebola virus disease has been found to be well-tolerated and produced immune system responses in all 20 healthy adults who received it in a Phase 1 clinical trial, researchers report.
The trials were conducted at US National Institutes of Health's clinical centre in Bethesda, Maryland.
The candidate vaccine is co-developed by the NIH's National Institute of Allergy and Infectious Diseases (NIAID) and GlaxoSmithKline (GSK).
"Based on these positive results from the first human trial of this candidate vaccine, we are continuing our accelerated plan for larger trials to determine if the vaccine is efficacious in preventing Ebola infection," said NIAID director Anthony S. Fauci.
The Ebola vaccine contains segments of Ebola virus genetic material from two virus species - Sudan and Zaire.
The Ebola virus genetic material is delivered by a carrier virus derived from chimpanzees that causes a common cold in chimpanzees but causes no illness in humans.
The candidate vaccine does not contain Ebola virus and cannot cause Ebola virus disease.
The trial enrolled volunteers between ages 18 and 50.
Ten volunteers received vaccine at a lower dose and 10 received the same vaccine at a higher dose.
At two weeks and four weeks following vaccination, the researchers tested the volunteers' blood to determine if anti-Ebola antibodies were generated.
All 20 volunteers developed such antibodies within four weeks of receiving the vaccine.
Antibody levels were higher in those who received the higher dose vaccine.
The investigators also analysed whether the vaccine prompted production of immune system cells called T-cells.
The experimental vaccine did induce a T-cell response in many of the volunteers including production of CD8 T cells which may be an important part of immune protection against Ebola viruses.
Four weeks after vaccination, CD8 T cells were detected in two volunteers who had received the lower dose vaccine and in seven of those who had received the higher dose.
"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," noted the trial's principal investigator Julie E. Ledgerwood.
