WASHINGTON (AP) — A top U.S. health official says long-anticipated clinical trials of a possible Ebola vaccine will start soon in West Africa. This word comes as the global response to the outbreak takes on added urgency with new cases in Mali and reports that the death toll has surpassed 5,000.

Dr. Anthony Fauci of the National Institutes of Health told Congress on Wednesday that results of an initial U.S. safety study proved promising enough that next-step testing should begin in Liberia and Sierra Leone by January.

Fauci says that if those new studies go well, health officials could know by the middle of 2015 whether or not there is an effective vaccine.

(Story by: Lauran Neergaard, Medical Writer, The Associated Press)