Almost 200 people have received GlaxoSmithKline's experimental Ebola vaccine in trials in the United States, Britain, Mali and Switzerland, and the safety data so far are "very satisfactory", scientists said on Monday.
The trials, which began just over two months ago, have been using healthy volunteers, rather than patients with Ebola, to test whether the vaccine is safe for humans.
The experimental shot uses a single Ebola virus gene from a chimpanzee virus to generate an immune response. Because it doesn't contain any infectious virus material, it can't infect those being vaccinated.
Adrian Hill, a professor at Oxford University who is leading the British arm of the trial, said 20 people at the U.S. National Institutes of Health in Bethesda, Maryland, 80 people at the University of Maryland School of Medicine Center for Vaccine Development in Mali, 34 people out of an eventual 120 at the University Hospital of Lausanne, and 59 out of an eventual 60 at the University of Oxford had so far been given the shot.
"The safety data here have looked very satisfactory so far," Hill said in a statement. "The response we have seen from people coming forward to take part has been remarkable."
The West Africa Ebola epidemic has now infected more than 13,000 people -- mainly in Guinea, Sierra Leone and Liberia -- and killed more than 5,000 of them, according to the World Health Organization (WHO).
Several drug companies are now accelerating Ebola vaccine trials and the WHO has said it hopes one or more of the vaccines may be ready for some limited use in West Africa in early 2015.
GSK's vaccine and another leading candidate made by NewLink Genetics are already in human trials. Five more should begin testing in the first quarter of next year, according to the WHO. One from Johnson & Johnson will start trials in January.
Hill said the teams running the GSK vaccine trial should know by late December 2014 how the immune responses of Malian health care workers who have had the shot compare to those observed in adults given the vaccine in Britain and Switzerland.