The experimental vaccine against Ebola is safe and may help the immune system to combat the virus, the first human trial results suggest.

Twenty volunteers were immunized in the US. Scientists at the US National Institutes of Health (NIH) described the results as “promising”.

The research is published in the New England Journal of Medicine (NEJM).

None of those immunized suffered major side-effects and all produced antibodies.

The volunteers were divided into two groups, receiving either a low or high dose. The antibody response was stronger among those receiving the higher dose.

The investigators found that seven of the high dose and two of the lose dose volunteers produced T-cell immune responses, which may be important in protection against Ebola viruses.

The vaccine uses a chimpanzee cold virus which has been genetically engineered to carry a non-infectious Ebola protein on its surface.

There are four trials underway of this experimental vaccine.

The US vaccine is bivalent – aimed at giving protection against the Sudan and Zaire strains of Ebola. It is the latter which is responsible for the current outbreak.

Trials of a monovalent vaccine – against the Zaire strain – are also underway in Oxford, Mali and Switzerland.

If these also yield positive results then the monovalent vaccine will be offered to thousands of health workers in West Africa.

If the vaccine does work, it is unclear how long the protection would last.

These kinds of questions are usually settled during the early stages of human trials.

In an editorial in the NEJM Dr. Daniel Bausch said that while the trial left many questions unanswered, an Ebola vaccine was “one step closer”.

The experimental vaccine is being manufactured by the British drugs giant GlaxoSmithKline (GSK).

GSK says it can produce one million doses a month by the end of 2015.

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