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Ebola Vaccine Candidate Safe and Immunogenic in Ground-Breaking Trial
Two experimental DNA vaccines to prevent Ebola virus and the closely related Marburg virus were safe and generated an immune response in healthy Ugandan adults that was similar to the response reported in healthy U.S. adults earlier this year. The findings, from the first trial of filovirus vaccines in Africa, were published in The Lancet.
“This is the first study to show comparable safety and immune response of an experimental Ebola vaccine in an African population,” said lead author Dr. Julie Ledgerwood of the National Institutes of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health. “This is particularly encouraging because those at greatest risk of Ebola live primarily in Africa, and diminished vaccine protection in African populations has been seen for other diseases.”
Scientists at the NIAID developed the DNA vaccines, which code for Ebola virus proteins from the Zaire and Sudan strains and from the Marburg virus protein. The vaccines contain the construction plans for the proteins on the outer surface of the virus. Immune responses against these proteins have been shown to be highly protective in non-human primate models.
The new phase I trial enrolled 108 healthy adults (aged 18 to 50 years) in Kampala, Uganda between November 2009 and April 2010. Each volunteer was randomly assigned to receive an intramuscular injection of the Ebola vaccine (30 volunteers), the Marburg vaccine (30), both vaccines (30), or placebo (18) at the start of the study, and again 4 weeks and 8 weeks later.
The investigators reported that the vaccines given separately and together were safe and stimulated an immune response in the form of neutralizing antibodies and T-cells against the virus proteins. Four weeks after the third injection, more than half of the volunteers (57% [17/30]) demonstrated an antibody response to the Ebola Zaire protein, as did 14 of 30 participants (47%) who received both the Ebola and Marburg vaccines. However, the antibodies were not long-lasting and returned to undetectable levels within 11 months of vaccination.
Both DNA vaccines were well-tolerated in Ugandan adults, with similar numbers of local and systemic reactions reported in all treatment groups. Only one serious adverse event (neutropenia) was reported in a Marburg vaccine-only recipient, but it was not thought to be vaccine-related.
“These findings have already formed the basis of a more potent vaccine, delivered using a harmless chimpanzee cold virus, which is undergoing trials in the U.S., U.K., Mali, and Uganda in response to the ongoing Ebola virus outbreak,” Ledgerwood said.
Sources: Medical Xpress; December 23, 2014; and Lancet; December 22, 2014.