Experimental Ebola Vaccine Seems Safe, Prompts Immune Response

Results from a Phase 1 clinical trial conducted by the U.S. National Institutes of Health (NIH) on a possible Ebola vaccine are leading to accelerated development of the candidate vaccine, NIH announced November 28.

The experimental vaccine to prevent Ebola virus disease was well-tolerated and produced immune system responses in all 20 healthy adults who received it, according to NIH.

The candidate vaccine, which was co-developed by the NIH’s National Institute of Allergy and Infectious Diseases (NIAID) and GlaxoSmithKline (GSK), was tested at the NIH Clinical Center in Bethesda, Maryland. The interim results were reported online in advance of print in the New England Journal of Medicine.

“The unprecedented scale of the current Ebola outbreak in West Africa has intensified efforts to develop safe and effective vaccines, which may play a role in bringing this epidemic to an end and undoubtedly will be critically important in preventing future large outbreaks,” said NIAID Director Anthony S. Fauci. “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.”

NIAID conducts and supports research — at NIH, throughout the United States, and worldwide — to study the causes of infectious diseases, and to develop better means of preventing, diagnosing, and treating them.

The candidate vaccine, developed collaboratively by scientists at the NIAID Vaccine Research Center and at GSK biotechnology company Okairos, contains segments of Ebola virus genetic material from two virus species, Sudan and Zaire.

The genetic material is delivered by a carrier virus (chimpanzee-derived adenovirus 3 or cAd 3) 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 the ages of 18 and 50. Ten volunteers received an intramuscular injection of vaccine at a lower dose and 10 received the 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 bigger dose of vaccine.

The investigators also analyzed the research participants’ blood to learn whether the vaccine prompted production of immune system cells called T cells. A recent study by NIH scientist Nancy J. Sullivan and colleagues showed that nonhuman primates inoculated with the candidate vaccine developed both antibody and T-cell responses, and that these were sufficient to protect the vaccinated animals from disease when they were later exposed to high levels of Ebola virus.

The experimental vaccine did induce a T-cell response in many of the volunteers, including production of CD8 T cells, which might 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 smaller dose of vaccine and in seven of those who had received the bigger dose.

There were no serious adverse effects observed in any of the volunteers, although two people who received the bigger dose did develop a brief fever within a day of vaccination.

The Phase 1 trial is the first step in a multi-stage process designed to ensure a vaccine approved for mass distribution will be effective and will not cause adverse health effects.

Phase 2 clinical trials will further assess safety and immune response in larger numbers of volunteers, and make additional progress on determining the vaccine’s ability to prevent infection (efficacy). Phase 3 clinical trials are directed at determining efficacy.

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