By Gene Emery

BOSTON, Feb 28 (Reuters) - An experimental vaccine can prevent more than 95 percent of infections with hepatitis E but its makers said on Wednesday they need to find a way to make it cheaply available in the poor countries that need it most.

An official of GlaxoSmithKline <GSK.N> <GSK.L>, which developed the vaccine in collaboration with the Walter Reed Army Institute of Research in Washington, D.C., said it likely will be five to seven years before further tests allow the company to seek licensing approval.

Little-known in developed countries, hepatitis E is a liver disease usually spread by contaminated water. It makes people sick for one to four weeks and is fatal for one out of 50 people. The death toll among pregnant women can be as high as 25 percent.

Hepatitis E was first recognized two decades years ago.

"It is the leading cause of jaundice and hepatitis among adolescents and young adults in most parts of the developing world but particularly in Asia and Africa," GlaxoSmithKline's Bruce Innis, one of the study's authors, said in a telephone interview.

The vaccine is most needed in areas of the world that may not be able to afford it.

Innis said the company is looking for a partner, such as a philanthropic foundation, to help make it available at a low price and explore whether it can be administered in combination with vaccines already given routinely to children.

The developers studied its effectiveness in 2,000 Nepalese soldiers in Kathmandu.

The virus is so common that 7 percent of the volunteers who received a placebo became ill just during the 30 months of the study.

But among the people who received an initial shot, plus two booster shots at one and six months, only 0.3 percent developed the nausea, abdominal pain, fatigue and loss of appetite that mark the onset of illness.

If only two doses were given, the effectiveness rate dropped to 85.7 percent, according to the results, published in the New England Journal of Medicine.

STOPPING THE SPREAD

But many questions remain. The researchers, for example, do not know how long immunity persists and they only looked at people who clearly became ill from the virus, known as HEV.

"It is conceivable, therefore, that the vaccine may not have prevented subclinical HEV infection," Krzysztof Krawczynski of the U.S. Centers for Disease Control and Prevention, wrote in a Journal commentary. "Asymptomatic HEV infection may be important because the vaccinated subjects without clinical symptoms may continue to shed virus and thus maintain an environmental reservoir of HEV."

Shedding virus means secreting it -- in this case, usually in feces.

In addition, nearly all the volunteers in the test were male. "It needs to be extended to women and to children because the logical way to support long-term disease prevention is to vaccinate children," Innis said.

"There needs to be continued development of the manufacturing process and tests of a commercial product on a commercial scale."

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