A one-shot version of a vaccine against Ebola fever provides protection after just 1 month, tests in monkeys show. If it proves safe to use in people, the fast-acting vaccine, deployed promptly, might help contain future Ebola outbreaks, scientists say in the Aug. 7 Nature.
Ebola is a highly contagious and often lethal viral infection. Including the first cases reported in 1976, nine outbreaks have sickened or killed hundreds of people in central Africa, according to the Centers for Disease Control and Prevention (CDC) in Atlanta. Wild primates are also susceptible.
Earlier, researchers tested a vaccine that entails three injections of Ebola DNA over 2 months, followed 12 weeks later by a booster shot of an adenovirus modified to carry genes for Ebola virus proteins. The adenovirus cannot replicate, but the Ebola proteins it makes grab the attention of the immune system, which were primed by the earlier exposure to Ebola DNA (SN: 12/2/00, p. 358).
While that two-step vaccine fostered impressive immunity in monkeys, it took several months to take hold, says Gary J. Nabel, a virologist at the National Institute of Allergy and Infectious Diseases in Bethesda, Md.
For the typical Ebola outbreak, that’s too slow, he says. So, Nabel and his colleagues injected eight cynomolgus macaque monkeys with an intramuscular shot of the gene-toting adenovirus. As a control group, five monkeys received an inert injection. A month after being vaccinated, the monkeys were injected with live Ebola virus.
All eight vaccinated animals survived; the other five monkeys died.
“This is real progress,” says virologist Joseph B. McCormick of the University of Texas Health Science Center in Brownsville. “The difference is quite clear between the controls and the vaccinated animals” in virus concentrations in the blood, as well as in overall survival.
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Nabel hopes to test both vaccine strategies on people by the end of 2004. If a
single-shot adenovirus vaccine proves safe to administer and engenders a potent immune defense, it might be useful in a ring-vaccination approach, he says.
Vaccinations would be given to people exposed to an infected person and also to others who spend time with those contacts.
While the vaccine appears “quite promising,” it may not work in immune-compromised people with HIV, a group that includes a vast population in central Africa, says immunologist Manisha Gupta of the CDC.
Also, the time between exposure to the virus and the onset of Ebola fever’s flulike symptoms and internal hemorrhaging is 7 to 21 days. Nabel says that animal tests are needed to reveal whether the vaccine derails Ebola virus if given during this time.
Ebola has a knack for popping up without warning, making it a public health nightmare, says William B. Karesh, a veterinarian at the Wildlife Conservation Society (WCS) in Bronx, N.Y. In an attempt to predict where new outbreaks will occur, WCS is training officials in central Africa to monitor deaths in wild primates and, when possible, to analyze the carcasses–using extreme precautions. Infected ape carcasses were found near the sites of two of Gabon’s four outbreaks seen since 1994, WCS biologist David S. Wilkie and his colleagues reported earlier this year. The outbreaks may have started after people ate infected ape meat.
Vaccinating wild gorillas and chimpanzees might seem a good way to slow the spread of Ebola but would be virtually impossible, says Wilkie. “Even trying to dart gorillas is hard,” he says, much less delivering an intramuscular injection.
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