Hepatitis E vaccine passes critical test.

An experimental vaccine for hepatitis E has proved nearly 96 percent protective in a test among soldiers in Nepal. The results set the stage for a final trial that could lead to commercialization of the vaccine, the first to be developed against this virus.

Other hepatitis vaccines don't work against hepatitis E, and there's no effective treatment for the disease that it causes. By some estimates, one-third of the world's population, mainly in Africa and Asia, has been infected at some time. A hepatitis E infection causes fatal liver failure in 1 to 3 percent of patients showing symptoms. Other signs of the disease are abdominal pain, nausea, fatigue, and yellowed skin.

The loss of wages from weeks or months of missed work creates a "huge burden" on families in poor countries where this hepatitis is endemic, says Bruce L. Innis, an infectious-disease physician at GlaxoSmithKline in King of Prussia, Pa.

Innis teamed with researchers from Nepal and the U.S. Army to recruit 1,794 Nepalese soldiers to test the vaccine. Half received three shots of the vaccine over 6 months, while the others got inert injections.

Over an average of 27 months, 3 volunteers who had received the full vaccine regimen came down with hepatitis E, compared with 66 soldiers who got the placebo, the researchers report in the March 1 Nay England Journal of Medicine. Tests on patients' blood or stool ascertained the viral infection.

"The vaccine practically knocks out the disease," says pathologist Krzysztof Krawczynski of the Centers for Disease Control and Prevention in Atlanta. He cautions that the researchers didn't measure whether vaccinated soldiers who appeared healthy were nonetheless infected with the virus. Such subclinical infections might create a group of people who, although feeling well, would spread the virus via their feces to untreated drinking-water sources such as streams.

"Many vaccines don't stop infection," counters Suzanne U. Emerson of the National Institute of Allergy and Infectious Diseases (NIAID) in Bethesda, Md. The successful vaccine fur hepatitis A falls in that category.

The main requirement of a vaccine is to prevent disease, which the new hepatitis E vaccine does, Emerson says. She and her NIAID colleagues fashioned the vaccine in 1994 from one of the virus' proteins.

Meanwhile, puzzles linger. Unlike many diseases, which prey mainly on children and old people, hepatitis E usually strikes people between 15 and 40 years of age. And despite probable exposure to hepatitis E in early childhood, people in endemic zones 'Tail to build up immunity to it--one of the enduring mysteries of hepatitis E," Innis says. Most troublesome is hepatitis E's high death rate--up to 25 percent-in pregnant women.

If the vaccine clears its final hurdle in a large-scale trial, Innis envisions a public health approach that targets adolescents and young adults--with extra efforts to reach girls before they enter childbearing years.

"Combining this with other vaccines would be a practical approach" that could cut costs, says study coauthor Mammen P. Mammen Jr., a U.S. Army infectious-disease physician at Fort Detrick in Frederick, Md.

It's unclear how long the vaccine's protection lasts. If immunity to hepatitis E wanes, Innis says, scientists might design a booster shot, as they did for the whooping cough vaccine.