By Lauren Raab, Melissa Healy, and Matt Pearce, Los Angeles Times

Tests of an experimental Ebola vaccine have shown positive results, protecting healthy monkeys from the virus, the National Institutes of Health announced Sunday, as West Africa grapples with an epidemic that has killed about 2,000 people.

Researchers gave four macaque monkeys a shot of the experimental vaccine, called ChAd3, and exposed them to high levels of the Ebola virus five weeks later. All the monkeys were protected, the NIH National Institute of Allergy and Infectious Diseases said.

The protection decreased over time, however: Ten months after receiving the vaccine, just two of the four were protected.

Researchers also tried giving monkeys the experimental vaccine and then, eight weeks later, a booster vaccine. Ten months after the initial dose, all four monkeys were fully protected, the institute said.

The authors of the latest study, published Sunday in the journal Nature Medicine, suggested that without the booster, the Ebola virus can quickly regain a foothold and attack the immune system.

Human safety trials of the ChAd3 vaccine were scheduled to start last week in Bethesda, Md., with preliminary results due by the end of 2014. In the current crisis, American officials overseeing the trials suggested that the availability of a tested vaccine would offer some assurance of protection to health-care workers wary of going to West Africa.

The experimental vaccine was developed by the pharmaceutical giant GlaxoSmithKline. The research team was led by Nancy J. Sullivan of the NIH and included scientists from Okairos, a biotechnology company that is now part of GlaxoSmithKline, and the U.S. Army Medical Research Institute of Infectious Diseases.

Separately, an Ebola-infected American doctor being treated in Nebraska has shown improvement but is still very ill, his wife said.

Dr. Rick Sacra, 51, an obstetrician who lives in the Boston area, contracted the deadly virus while treating patients in Liberia as part of a missionary program. He was flown to the Nebraska Medical Center in Omaha on Friday.

This year’s Ebola outbreak is the worst on record, with a fatality rate of 53 percent, according to the World Health Organization.

Rick Sacra is the third American to be transported to the United States this year after contracting the virus.

Nancy Writebol and Dr. Kent Brantly, who were also missionaries in Liberia, recovered after treatment at a special infectious-disease unit at Emory University Hospital in Atlanta. Writebol and Brantly received an experimental medication, ZMapp, but it is unclear whether that helped them.

In all, seven Ebola patients received ZMapp. Five were later released from hospitals; the other two did not survive. The company that developed the drug, Mapp Biopharmaceutical Inc. of San Diego, says it has no doses left. Making it is time-consuming, but the U.S. is trying to help the company speed up the process.

There is no cure or approved vaccine for Ebola, which triggers hemorrhaging and is transmitted through contact with the bodily fluids of those infected. The latest outbreak was first detected in Guinea in March and has since affected Liberia, Sierra Leone, Nigeria and Senegal, where at least one patient has been identified.

Times staff writer Alexandra Zavis contributed to this report.

AFP Photo/Zoom Dosso

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