Washington: The first trial of an experimental Ebola vaccine in Africa has shown it is safe for use, scientists say. “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 from the National Institutes of Allergy and Infectious Diseases (NIAID) at the National Institutes of Health, US.
“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,” Ledgerwood said.
Scientists from the NIAID developed two experimental DNA vaccines that code for Ebola virus proteins from the Zaire and Sudan strains and the closely related Marburg virus protein.
Like the Ebola virus, Marburg is a filovirus that causes internal bleeding at multiple sites with patients usually dying as a result of multiple organ failure. Currently, no effective vaccines against either virus exist. The experimental vaccines contain the construction plans for the proteins on the outer surface of the virus.
Immune responses against these proteins have shown to be highly protective in non-human primate models. In this phase 1 trial, the results of which are published in The Lancet, the Makerere University Walter Reed Programme enrolled 108 healthy adults aged between 18 and 50 from Kampala, Uganda between November, 2009 and April, 2010, researchers said.
Each volunteer was randomly assigned to receive an intramuscular injection of either the Ebola vaccine (30 volunteers), Marburg vaccine (30), both vaccines (30), or placebo (18) at the start of the study, and again 4 weeks and 8 weeks later.
The vaccines given separately and together were safe and stimulated an immune response in the form of neutralising antibodies and T-cells against the virus proteins. Four weeks after the third injection, just over half of the volunteers (57 per cent) had an antibody response to the Ebola Zaire protein as did 14 of 30 participants 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 groups.
“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 US, UK, Mali, and Uganda in response to the ongoing Ebola virus outbreak,” said Ledgerwood. According to the World Health Organisation, Ebola has killed more than 7,500 people in Guinea, Liberia and Sierra Leone.