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TUESDAY, Dec. 23, 2014 (HealthDay News) -- There's good news about the experimental Ebola vaccine that U.S. officials are preparing to test in West Africa -- new research shows a precursor of that vaccine produced a safe and potent immune response in Africans.
That earlier version of the vaccine, when given to more than 100 Ugandans in 2009 and 2010, prompted the production of antibodies and white blood cells that could potentially protect a person against infection by Ebola, said study author Dr. Julie Ledgerwood, chief of the clinical trials program in the U.S. National Institute of Allergy and Infectious Diseases' Vaccine Research Center.
"This is the first study to show comparable safety and immune response of an experimental Ebola vaccine in an African population," Ledgerwood said. "This is particularly encouraging because those at greatest risk of Ebola live primarily in Africa, and diminished vaccine protection in African populations has been seen for other diseases."
The vaccine uses the chimp virus to deliver pieces of Ebola genetic material to human cells, which hopefully will prompt an immune response that protects against infection.
The earlier vaccine used a less efficient DNA-based carrier to deliver the exact same Ebola genetic material that's contained in the new vaccine, Ledgerwood explained. She and her colleagues report results from the earlier trial in the Dec. 23 online issue of The Lancet.
"DNA gets into human cells pretty well, but chimp adenovirus gets into the human cell very well," she said. "It's a better delivery system."
Thus, the success of the earlier vaccine provides some hope that the new NIH vaccine will be safe for Africans and produce an immune response in them similar to that found in Americans during prior safety trials, Ledgerwood said.
The ongoing Ebola outbreak in West Africa has claimed 7,373 lives, according to the World Health Organization. The total number of cases in Guinea, Sierra Leone and Liberia now stands at 19,031.
Dr. Tom Frieden, director of the U.S. Centers for Disease Control and Prevention, just returned from a second visit to West Africa where he met with CDC staffers, health officials and the presidents of the three countries hit hardest by the virus.
During a news conference held on Monday, Frieden described progress in some areas but growing numbers of Ebola cases in other parts of West Africa.
"In Liberia, the outbreak has slowed dramatically and at the moment the country has the upper hand against the virus, in part due to improvements in access to [treatment centers and clinics], safe burials and community engagement," Frieden said.
"But the outbreak continues to surge in Sierra Leone, and there has been a troubling spread in Guinea's capitol city. We've got a long way to go and this is no time to relax our grip on the response," he added.
"CDC staff are committed to this cause because they understand the urgency in stamping out Ebola in West Africa," Frieden said. "Stopping this outbreak at its source in West Africa is essential in order to protect Americans. That is why CDC is on the ground."
In the precursor vaccine trial just reported in The Lancet, more than 108 healthy adults aged 18 to 50 from Uganda were randomly assigned between November 2009 and April 2010 to receive either the Ebola vaccine, a similar vaccine designed to prevent deadly Marburg virus, both vaccines at the same time or an inactive placebo.
Participants received a series of three shots over eight weeks, and then researchers tracked their health and immune system response.
Both vaccines proved safe when given either separately or together, and both produced an immune response, the researchers reported.
About half of the participants developed antibodies in response to the Ebola vaccine, which targeted two different strains of the virus, and the Marburg vaccine, the investigators found.
One expert praised the results.
"That the Ebola part of the trial was with a vaccine that protects against the Sudan and the Zaire strains is significant, because a vaccine which is protective against more than one strain of Ebola will be very advantageous," said Dr. Amesh Adalja, a senior associate at the UPMC Center for Health Security in Baltimore.
However, the antibodies created from the vaccine were not long-lasting, the researchers found, and returned to undetectable levels within 11 months of vaccination.
That waning protection was expected, Ledgerwood said. In a DNA-based vaccine, continuing protective levels of antibodies usually don't occur unless people receive some sort of booster. They expect the chimp virus Ebola vaccine to produce a stronger and more lasting response.
NIH researchers are preparing to go back to the same group of Ugandans and offer to boost their earlier Ebola vaccinations using the new chimp virus-based vaccine, Ledgerwood said.
"We expect that will teach us a few things about Ebola virus immunology," Ledgerwood said.
A rival Canadian vaccine for Ebola also is about to begin clinical trials in West Africa. The Canadian vaccine uses a virus common to cattle and horses called vesicular stomatitis virus (VSV), which is in the same viral family as the rabies virus but causes only flu-like symptoms in infected humans.
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SOURCES: Julie Ledgerwood, D.O., chief, clinical trials program, U.S. National Institute of Allergy and Infectious Diseases' Vaccine Research Center; Amesh Adalja, M.D., F.A.C.P., senior associate, UPMC Center for Health Security, Baltimore; Dec. 23, 2014, The Lancet, online