WEDNESDAY, Nov. 26, 2014 (HealthDay News) -- An experimental Ebola vaccine appears to be safe and produces an immune system response that could protect people against the deadly virus, according to early clinical trial results reported by the U.S. National Institutes of Health.
The success of the phase I clinical trial for the vaccine paves the way for field-testing it in the Ebola-stricken West African nations of Liberia and Sierra Leone as early as January, said Dr. Anthony Fauci, director of the NIH's National Institute of Allergy and Infectious Diseases.
The genetically engineered vaccine caused no major side effects in 20 healthy adults who received a dose in September at the NIH Clinical Center in Bethesda, Md., the researchers report in the Nov. 26 issue of the New England Journal of Medicine.
The vaccine also created an immune system response in humans very similar to that of monkeys who, once inoculated, survived lab tests that exposed them to potentially fatal doses of Ebola, Fauci said.
"All in all, one can say this is a successful vaccine, from the standpoint of phase I," Fauci said. "Now the critical question is, will it work?"
Ebola has killed more than 5,450 people during the West African epidemic, according to the World Health Organization. In response, international efforts to develop a preventive vaccine have accelerated.
The current vaccine, developed by the Institute of Allergy and Infectious Diseases and GlaxoSmithKline, is based on a virus called chimpanzee-derived adenovirus, which causes a common cold in chimps but has no effect on humans.
Researchers have spliced portions of Ebola's genetic material into the chimp virus, to trick the immune system into creating Ebola-attacking antibodies without exposing the body to the virus itself.
The clinical trial enrolled volunteers aged 18 to 50. Ten volunteers received a low-dose injection of the vaccine, while another 10 received the same vaccine at a higher dose.
Within a day of vaccination, two people who got the higher dose developed a fever, which was "short-lived and easily handled," Fauci said.
"There were no real red flags when it comes to safety," he said.
At two weeks and four weeks following vaccination, the researchers tested the volunteers' blood to determine if anti-Ebola antibodies were generated. All 20 volunteers developed such antibodies within four weeks of receiving the vaccine, but antibody levels were higher in those who received the higher-dose vaccine.
"The results of the vaccine trial are promising and show that this particular vaccine is able to induce protective levels of immunity," said Dr. Amesh Adalja, a senior associate with the Center for Health Security at the University of Pittsburgh Medical Center. "The trial also begins to provide a basis for selecting the optimal dose needed to achieve protection against Ebola."
Two other phase I trials for the vaccine are ongoing in the United Kingdom and Mali, with results expected by year-end, the NIH said.
But based on the success of the Bethesda trial, researchers hope to begin delivering the experimental vaccine to people in Liberia and Sierra Leone within a couple of months, Fauci said.
Fauci could not say how many people would receive the vaccine in the field trials. "We don't have the exact number," he said. "In order to determine efficacy, you'll have to vaccinate thousands of people, not just hundreds of people."
The vaccine in question is one of two experimental Ebola vaccines that experts have said could be ready in time to combat the current epidemic.
The second vaccine, also genetically engineered, is based on a virus common to cattle and horses called vesicular stomatitis virus (VSV). This is in the same family as the rabies virus but causes only flu-like symptoms in infected humans.
Produced by the Public Health Agency of Canada based on research by NewLink Genetics of Iowa -- the second vaccine is also being tested in phase I trials.
Thomas Geisbert, an Ebola expert and a professor of microbiology and immunology at the University of Texas Medical Branch, believes the VSV-based Ebola vaccine may be the way to go.
Although clinical trial results for the NIH/GlaxoSmithKline vaccine are "promising," other experimental Ebola vaccines based on chimp adenovirus have not provided protection against more aggressive strains of the virus, he said.
Geisbert believes the vaccine pursued by Canadian researchers could be more effective and produce longer-lasting protection.
"It remains to be seen if they are equally or nearly equally as safe," Geisbert said. "If it turns out that they are, then I think the VSV-based vaccines will be the front runners."
For more on Ebola virus, visit the U.S. Centers for Disease Control and Prevention.