For the Ebola outbreak currently sweeping across West Africa, a vaccine that could provide immunity to individuals who are at high risk of contracting the fatal disease could mean life and death. It could also play a crucial part in ending the outbreak that the World Health Organization has described to be the worst in history.

Such vaccine is not yet widely available as most Ebola vaccines are still in their experimental and development phase. A vaccine that is now currently tested in human trials, however, has shown promising results in an experiment with monkeys raising hopes that the same could be achieved in the trials involving human subjects and which could mean that the vaccine may soon be safely recommended for individuals who are at risk of contracting the fatal hemorrhagic fever.

For the trial that involved monkeys, which was published in the journal Nature Medicine on Sept. 7, Nancy Sullivan, from the U.S. National Institute of Allergy and Infectious Diseases (NIAID) and colleagues found that a single shot of the experimental vaccine induces protection in all of the vaccinated monkeys and protected them when they were exposed to the Ebola virus five weeks later.

Only half of the monkeys, however, still had immunity ten months after the vaccination so the researchers tried the "prime-boost" approach which involved injecting a dose of the chimp virus-based vaccine to jumpstart the monkeys' immune system and giving them a booster shot of a differently-prepared vaccine after two months.

The researchers found that the second approach provided all of the Ebola-infected monkeys in the study immunity ten months after their initial shot.

"Here we show that a chimpanzee-derived replication-defective adenovirus (ChAd) vaccine also rapidly induced uniform protection against acute lethal EBOV challenge in macaques," the researchers wrote. "Because protection waned over several months, we boosted ChAd3 with modified vaccinia Ankara (MVA) and generated, for the first time, durable protection against lethal EBOV challenge."

Thomas Geisbert, from the University of Texas Medical Branch at Galveston, said that while the booster approach resulted in longer-lasting immunities in the monkey trial, he doubts that it would work in an Ebola outbreak because there would be not enough time to prime and boost the body's immune system.

"You really need a fast-acting single-injection vaccine that you can give to health care workers and first responders right before you send them into the hot zone," he said.

Two women were already given the experimental vaccine, which was developed by NIAID and pharmaceutical company GlaxoSmithKline, last week in a human trial that aims to assess its safety and efficacy.

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