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WASHINTON, D.C. -- A single shot of a fast-acting, experimental Ebola vaccine successfully protects monkeys from the deadly virus after only one month. If this vaccine proves similarly effective in humans, it may one day allow scientists to quickly contain Ebola outbreaks with ring vaccination - the same strategy successfully used in the past against smallpox, according to a study published in this week's issue of Nature.
This finding is the result of collaboration between scientists at the Dale and Betty Bumpers Vaccine Research Center (VRC), part of the National Institute of Allergy and Infectious Diseases (NIAID), and scientists at the United States Army Medical Research Institute of Infectious Diseases (USAMRIID) at Fort Detrick, Md.
"This research has enormous public health implications not only because it might be used to limit the spread of Ebola virus, which continues to emerge in central Africa, but also because this vaccine strategy may be applied to other highly lethal viruses, such as the Marburg and Lassa fever viruses and the SARS coronavirus, that cause acute disease outbreaks and require a rapid response," says NIAID Director Anthony S. Fauci, MD.
Under the directorship of Gary Nabel, MD, PhD, scientists at the VRC have been pursuing the so-called "prime-boost" vaccine strategy against a variety of infectious diseases. Prime-boost is a two-part process: First, an injection of non-infectious genetic material from the disease-causing microbe primes the immune system to respond. Second, several weeks later, an injection of attenuated carrier viruses containing key genes from the microbe substantially boosts the immune response.
The VRC scientists found that the boost alone produces a quicker but weaker immune response as compared with the prime-boost strategy. Knowing that time is critical when fighting Ebola, the scientists decided to test whether the boost's fast response was strong enough on its own to protect against the disease. To perform this test, they collaborated with colleagues at USAMRIID, who had the necessary facilities and expertise and who had developed good animal models for the experiment.
The VRC scientists immunized eight monkeys with a single boost injection, consisting of attenuated carrier viruses containing genes for important Ebola antigens. The monkeys were then delivered to USAMRIID where they were injected with an Ebola virus strain obtained from a fatally infected person from the former Zaire in 1995. The single vaccine injection completely protected all eight animals against Ebola infection, even those who received high doses of the virus.
"I am proud that our research team at USAMRIID was able to form an effective partnership with our colleagues at NIAID to develop and evaluate this Ebola vaccine," comments Peter B. Jahrling, PhD, senior research scientist at USAMRIID. "After years of developing candidate Ebola vaccines that protected rodents but failed in primates, it is gratifying to have a vaccine that holds great promise for protection of humans. Eventually, this vaccine may reduce the hazard of working with Ebola virus in the laboratory, as well as provide protection to populations at risk of natural exposure."
Ebola virus spreads easily from person to person, causes illness quickly and kills a significant number of the people it infects. There is no treatment for the disease, so preventing the spread of the virus is key to containing outbreaks. If the results of this animal study hold true for humans, the new vaccine may be just the Ebola-fighting tool that public health officials need during epidemic outbreaks, Nabel explains.
"Ring vaccination might be used to stop the spread of the Ebola virus during acute outbreaks, just as this strategy was used to contain smallpox in the past," Nabel says. With ring vaccination, everyone who has been in contact with a patient, as well as all members of the patient's household, are vaccinated. The ring strategy, which requires a fast-acting vaccine, not only protects people who may have been exposed to the virus but also creates an added barrier of immunity around them, thereby protecting the entire community.
Even though the boost alone appears to be effective, the prime-boost strategy, which requires four shots over six months, will still be important to pursue as well, Nabel says. "The prime-boost strategy elicits a stronger immune response," he explains, "and it may be useful for preventive vaccines intended for hospital workers at high risk of exposure to the virus, for example."
NIAID is a component of the National Institutes of Health (NIH), which is an agency of the Department of Health and Human Services. NIAID supports basic and applied research to prevent, diagnose, and treat infectious and immune-mediated illnesses, including HIV/AIDS and other sexually transmitted diseases, illness from potential agents of bioterrorism, tuberculosis, malaria, autoimmune disorders, asthma and allergies.
Reference: Sullivan N., et al. Accelerated vaccine for Ebola virus hemorrhagic fever in non-human primates. Nature. 424(6949):681-84 (2003).
Source: National Institutes of Health