WASHINGTON (AP) — Federal researchers next week will start testing humans with an experimental vaccine to prevent the deadly Ebola virus.

The National Institutes of Health announced Thursday that it is launching the safety trial on a vaccine developed by the agency's National Institute of Allergy and Infectious Diseases and GlaxoSmithKline. It will test 20 healthy adult volunteers to see if the virus is safe and triggers an adequate response in their immune systems.

That testing will be at NIH's campus in Bethesda, Maryland. Later in September, NIH and a British team will test that vaccine on volunteers in the United Kingdom, Gambia and Mali.

American health officials are also talking about a future trial in Nigeria.

So far Ebola has killed 1,552 people in West Africa.