This latest study is the first to report promising findings for an Ebola vaccine in an African population, according to the researchers.
Both Ebola and Marburg belong to a family of viruses called Filoviridae, or filoviruses, which are known to cause severe hemorrhagic fever in both humans and nonprimates. There are five species of Ebola virus; the Zaire (EBOV) and Sudan (SUDV) strains are behind the 2014 outbreak. Marburg is a single-strain virus.
In their phase 1 clinical trial, led by Dr. Julie Ledgerwood of the National Institutes of Allergy and Infectious Diseases (NIAID), the team tested the effectiveness of two vaccines - one for the EBOV and SUDV strains of Ebola (EBO vaccine) and one for Marburg (MAR vaccine) - in 108 healthy participants aged 18-50 from Kamapala, Uganda, between November 2009 and April 2010.
The vaccines, created by researchers from the NIAID, are made up of protein structures on the outer surface of the viruses. These generate an immune response in the body but do not allow viral replication.
Effectiveness and safety of vaccines 'particularly encouraging'
At study baseline and at 4 and 8 weeks later, participants were randomly assigned to receive an injection of either the EBO vaccine, the MAR vaccine, both vaccines or a placebo.
The team found that the EBO and MAR vaccine - when administered separately and together - effectively triggered an immune response in participants by neutralizing antibodies and T cells against the proteins of the viruses.
Among participants who received the EBO vaccine, 17 of 30 displayed an antibody response to the Ebola Zaire protein 4 weeks after the last injection, while 14 of 30 participants who received both the EBO and MAR vaccine showed an antibody response against the protein. The researchers note, however, that these antibodies were at undetectable levels within the following 11 months.
Both of the vaccines were well tolerated by participants, the researchers say, with only one adverse reaction - a low white blood cell count - reported in one participant who received the MAR vaccine only. This case, however, was not believed to be triggered by the vaccine.
Commenting on the team's findings, Dr. Ledgerwood says:
"This is the first study to show comparable safety and immune response of an experimental Ebola vaccine in an African population. 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."
Results have already boosted clinical testing of another Ebola vaccine
Dr. Ledgerwood notes that the results of this study have already "formed the basis" and boosted clinical testing of another Ebola vaccine, known as cAd3-EBO, which is delivered using a chimpanzee "cold" virus.
Reported by Medical News Today in September, the vaccine was revealed to have induced long-term immunity against Ebola in monkeys, which led the National Institutes of Health to announce the vaccine would be entering phase 1 clinical trials in the US. It is also entering expanded trials in Europe and Africa.
In an editorial linked to this latest study, Dr. Saranya Sridhar, of the Jenner Institute at the University of Oxford in the UK, says the findings should be a "focal point" for Ebola vaccine development.
"With the uncharitable benefit of hindsight in view of the evolving 2014 Ebola outbreak, we must ask ourselves whether a filovirus vaccine should have been in more advanced clinical development," she says, adding:
"The international response to the present Ebola outbreak is an exemplar of the speed and purpose with which clinical vaccine development can progress and has set the benchmark against which future vaccine development must be judged.
This study is the first step on the aspirational road toward the deployment of filovirus vaccines in Africa and must serve to shake the metaphorical cobwebs that can stall our advance toward this destination."
A recent report, also published in The Lancet, reveals how a doctor who contracted Ebola in Sierra Leone was successfully treated with a drug called FX06, which is currently undergoing testing for use against vascular leakage syndrome.