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The first-ever trial of an Ebola vaccine in Africa showed promising initial results, reports the Lancet medical journal.

The vaccine, given to Ugandan and American volunteers, appeared to generate the desired immune response - although not enough to make it a good candidate for wider use.

Scientists say although it will not beat Ebola, it is a crucial step.

This trial has stopped but other vaccines are in development.

The Ebola virus has killed more than 7,000 people in the worst-affected countries of Sierra Leone, Liberia and Guinea.

No proven vaccine exists to prevent people from getting the disease, though several trials are underway.

The aim of a successful vaccine is to train the immune systems of healthy people to produce antibodies - proteins capable of fighting off any future infections.

The Lancet study

In 2009, researchers from the National Institutes of Health (NIH) tested their experimental vaccine on healthy adults in Uganda, having first trialled it in the US.

Dr Julie Ledgerwood, the lead researcher of the trial that has been written up and published in The Lancet, said: "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."

According to the study some 57% of people in Uganda who received the Ebola vaccine alone developed antibodies against Ebola in their blood.

Dr Sridhar of the University of Oxford, commenting on the research, said the data provided insights into Ebola vaccine development.

Vaccines currently being tested against Ebola are made in a different way to the NIH one.