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Fast-Acting Vaccine Blocks Ebola Virus

Quicker protection may aid outbreak control

(HealthDay is the new name for HealthScoutNews.)

WEDNESDAY, Aug. 6, 2003 (HealthDayNews) -- A fast-acting version of the Ebola vaccine builds protection against the deadly virus in one month instead of the usual six and could make containment of the pathogen more realistic, a new study says.

The new vaccine is still experimental and it hasn't yet been tested in people. But it could help public health workers control outbreaks of the disease more quickly and effectively. "We're probably going to go back and see just how much we can press the envelope. You'd want to immunize [health workers] today and put them on a plane tomorrow," says study co-author Peter Jahrling, an Ebola expert at the U.S. Army Medical Research Institute of Infectious Diseases.

A fast-working vaccine not only would benefit health workers, but it could let them corral an outbreak using so-called "ring" vaccination -- the process of inoculating contacts of infected people. A report on the findings appears in the Aug. 7 issue of Nature.

Ebola was first identified in 1976 and has plagued Africa since. The disease is caused by two of four fluid-borne viruses that produce a fatal, bleeding fever. They kill roughly 80 percent of the people they infect, usually within a week. Its status as one of the world's deadliest and most gruesome viruses makes Ebola an obvious choice for bioterrorists.

Scientists have had success creating a vaccine that stimulates the immune system against Ebola. But the battery of shots -- which uses DNA from the virus along with boosters -- takes more than six months to administer fully, too long to be much help against a blitzing outbreak.

In the new study, researchers at the National Institutes of Health and the U.S. Army's Medical Research Institute of Infectious Diseases tried to streamline the Ebola vaccine. They eliminated the first step, relying instead simply on a version of the booster -- a mix of crippled adenoviruses (a form of cold virus) carrying three genes for harmless proteins from the deadly microbe's Zaire strain.

"What is very attractive about the adenovirus is that it seems to be very well adapted towards eliciting strong immune responses," says Dr. Gary Nabel, director of the National Institutes of Health's Vaccine Research Center in Bethesda, Md., and leader of the research project.

Macaques that received the vaccine quickly began producing blood proteins specific to Ebola, an important step in building immunity to the virus. The reaction was weaker than with the DNA-based vaccine, but it was faster. What's more, the single injection was strong enough to protect every animal from infection with the virus 28 days later, the researchers say.

That's about the standard for vaccines against diseases such as measles and mumps, though the smallpox vaccine is believed to provide protection in as little as four days, Jahrling says. "We're not going to get that for sure, but it's not unprecedented to get it down to a week."

"We have not tested the lower limits of protection in terms of the time interval between the first shot and the ultimate challenge" with Ebola, Nabel says.

"It looks to be a very effective vaccine. A single shot protects the monkeys completely," says Dennis Burton, an immunologist at the Scripps Research Institute in La Jolla, Calif. "It's very impressive." Burton calls the chances the shot will work in humans "very high."

Last year the Dutch firm Crucell NV announced it was partnering with the National Institutes of Health to develop an Ebola vaccine. The vaccine will use Ebola genes sewn into a crippled cold virus. Nabel's group also is working with the California firm Vical to bring their DNA-based vaccine to market.

Since Ebola is so lethal, whatever vaccines against the microbe win regulatory approval will do so thanks to effectiveness tests on lab animals, and monkeys in particular, rather than people. But the sacrifice doesn't have to be in vain.

Ebola's Zaire strain is now decimating the great ape populations in Africa, especially in Gabon and the Republic of Congo. A recent study in Nature claims the virus now rivals hunting and logging in the demise of gorillas and chimps, whose numbers fell by more than half in Gabon between 1983 and 2000.

"Maybe this is a way to save those great apes," says Jahrling. "There are no known adverse events" associated with the inoculation, he says, and there's no reason to believe it would harm the animals.

However, conducting a rigorously controlled clinical study of the vaccine in wild apes would be impossible, Jahrling says. "It's not trivial to go up to an ape and find out if he has Ebola," Nabel adds. So scientists may have to be especially creative to bring the vaccine to the creatures.

More information

Try the World Health Organization or the U.S. Centers for Disease Control and Prevention to learn more about Ebola.

SOURCES: Gary Nabel, M.D., Ph.D., director, Vaccine Research Center, National Institutes of Health, Bethesda, Md.; Peter Jahrling, Ph.D., senior research scientist, U.S. Army Medical Research Institute of Infectious Diseases, Fort Detrick, Md.; Dennis Burton, Ph.D., professor of immunology, Scripps Research Institute, La Jolla, Calif.; Aug. 7, 2003, Nature
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