It will take five or six years to complete the research to show the experimental vaccines can be safe and effective for people exposed to the contagious viruses, which are almost always fatal, said Steven Jones, one of the Canadian-based scientists behind the study.

A health worker in Uige, Angola, leaves a makeshift tent used to treat Marburg victims earlier this year.

"The data would suggest that instead of 100 percent chance of dying, they would have an 80 percent chance of survival," Jones said.

It is the first sign of success for a Marburg vaccine. Dutch company Crucell is working on commercializing a different type of Ebola vaccine.

Marburg and Ebola viruses are spread by bodily fluids including blood, sweat and saliva. Most victims die within days after massive bleeding.

Jones and collaborator Heinz Feldmann have been part of an international relief effort for the world's worst outbreak of Marburg virus in Uige, Angola, where 335 of 399 people who contracted the disease had died as of May 26, according to the World Health Organization.

Protecting family members

There is no vaccine or treatment other than drugs to relieve pain for victims, said Jones, who will return to Angola this week.

"One of the most nasty, foul things about this disease is that it is spread by close contact," he said, noting it often kills relatives of the ill.

"If you could use this vaccine in the field and vaccinate family members of known cases, you could be protecting those people who are putting their lives at risk for their loved ones," Jones said.

Work on the vaccine began more than three years ago at Canada's National Microbiology Laboratory in Winnipeg, Manitoba.

Jones and Feldmann replaced a protein in an animal virus with a protein from the Ebola and Marburg viruses, and successfully tested the vaccines on rodents.

The U.S. Army Medical Research Institute of Infectious Disease in Maryland injected monkeys with the vaccines, and then 28 days later with the viruses.

The monkeys survived.

"Monkeys, when they are infected, suffer almost the identical disease to humans," Jones said. "If we can protect them using this vaccine ... then this gives us a good deal of confidence that this will work in humans."

The new Ebola vaccine has some advantages, said Thomas Geisbert, a top virologist with the U.S. Army Medical Research Institute of Infectious Disease.

It is a live vaccine that grows inside the recipient for a short period of time, generating a rapid and strong immune response, Geisbert said.

"You wouldn't necessarily have to revaccinate or boost individuals every year or two," he said, noting the effects could last for five years or more.

The team will now produce the vaccines in a regulated facility, and repeat studies to ensure they work and are safe.

Researchers also need to determine how quickly the vaccines take effect. Jones said trials demonstrated protection in 28 days, but speculated the vaccines could work in half that time.

The research has been financed by the Canadian government and U.S. military, which want vaccines in case of a domestic outbreak or a biological attack by terrorists, Jones said.

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