Results of the phase I clinical trial of an Ebola vaccine brings good news particularly to countries being ravaged by the fatal virus.

Researchers reported on Nov. 26 that an experimental vaccine for Ebola, designed to boost the immune system's production of antibodies that fight the virus, appears to be safe and trigger an immune response in the first human trial involving 20 healthy volunteers between 18 and 50 years old.

For the clinical test of the vaccine dubbed cAd3-EBO, Julie Ledgerwood from the National Institute of Allergy and Infectious Diseases (NIAID), together with colleagues, injected the volunteers with the vaccine in September to assess its safety and determine if it provides protection against the Zaire strain of the virus responsible for the current epidemic in West Africa and the Sudan Ebola.

Half of the participants received a dose 10 times more than the other 10 volunteers received. The researchers then tested the blood of the volunteers weeks after the vaccination to find out if anti-Ebola antibodies were produced.

They found that all of the volunteers developed the antibodies four weeks after they were given the experimental vaccine. Those who were administered the higher dose had a higher antibody concentration than those who were given a lower dose.

"Reactogenicity and immune responses to cAd3-EBO vaccine were dose-dependent," the researchers reported in the New England Journal of Medicine on Nov. 26. "At the 2×1011 particle-unit dose, glycoprotein Zaire-specific antibody responses were in the range reported to be associated with vaccine-induced protective immunity in challenge studies involving nonhuman primates."

Ledgerwood and colleagues also conducted an analysis on the blood samples of the participants to determine if the vaccine triggered the production of T-cells, a type of white blood cell with key roles in the body's immune system. Findings revealed that the vaccine, which was collaboratively developed by NIAID and GlaxoSmithKline (GSK), indeed prompted T-cell response.

CD8 T cells, which are believed to be an important component of immunity against the Ebola disease, were also detected in nine volunteers four weeks after vaccination.

"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," Ledgerwood said. "The CD8 T cell response we saw in this trial are similar to that observed in non-human primates vaccinated with the candidate vaccine."

Although the investigators did not find serious side effects, two of the volunteers had fever after administration of the vaccine.

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