The first human trials of a vaccine against Ebola have been successful, but it will be months, at best, before it can be used to stem the outbreak in West Africa.

The origins of the vaccine go back more than a decade. A chimpanzee cold virus was modified to carry Ebola genetic material conferring protection against the Zaire strain of Ebola. This was shown to be effective in monkeys, although the benefits wore off with time.

Progress was delayed not by technical obstacles but economics. Previous outbreaks were controlled by tracing and quarantining the sick. With the people most endangered also being the least able to pay, funding was limited.

Recent events, however, changed the timelines and trials are scheduled to begin next year. "The unprecedented scale of the current Ebola outbreak in West Africa has intensified efforts to develop safe and effective vaccines," said renowned infectious disease researcher Dr. Anthony Fauci of the National Institute of Allergy and Infectious Diseases. The institute is producing the vaccine in partnership with GlaxoSmithKline.

The Phase I trial saw 20 volunteers injected with the vaccine in September. Two suffered mild fevers but none got seriously ill. Within four weeks, all were producing Ebola antibodies. Half the group received a dose ten-times larger than the rest, which resulted in greater antibody concentrations.

Besides the antibodies, researchers were keen to see evidence of CD8 T immune cells. "We know from previous studies in non-human primates that CD8 T cells played a crucial role in protecting animals," said first author Dr. Julie Ledgerwood. The vaccine is not triggering CD8 T cell production on a reliable basis, but seven of those on the higher dose and two on the lower started producing the cells, Ledgerwood reports in The New England Journal of Medicine.

The trial was designed to provide protection both against the Zaire strain currently ravaging West Africa, as well as Sudan Ebola. Some of the participants only produced antibodies against one or other strain, but most showed responses to both. Two other vaccines, one targeting Zaire Ebola alone, are also in Phase I human trials.

Two weeks ago, Fauci expressed hope that field trials to help those at high risk of contracting the virus will begin in January. Efforts to slow the outbreak's spread have been more successful than was predicted in September when the Centers for Disease Control estimated 1.4 million infections by January in a worst case scenario. Nevertheless, infection rates are still soaring in Sierra Leone, and only a vaccine is likely to finally stop the deaths.