The experimental vaccines also showed promising results when given orally or as an aerosol to mice. Both forms would make administering the vaccine easier in areas with poor public health systems.

Because humans and monkeys have similar immune systems, researchers are optimistic the vaccine will work in humans, said Steven Jones, a researcher at Canada's Public Health Agency in Winnipeg and coauthor of the study.

There are no known cures for the two diseases, which cause high fever, massive bleeding and death for the vast majority of those infected. If the vaccines are found to be safe and effective for people, they could be approved for limited use in two or three years.

Genetic Engineering Techniques

The research, published in the journal Nature Medicine, comes as the largest outbreak ever of Marburg hemorrhagic fever rages in Angola. So far, 335 people there have died from the disease, according to the World Health Organization. An Ebola outbreak in the Republic of the Congo also has claimed nine lives in the last few weeks, according to the organization.

The vaccines were developed using genetic engineering techniques to insert selected Ebola and Marburg genes into a harmless virus. The altered virus replicated in test animals and produced proteins that stimulated a strong immune response.

Researchers at the U.S. Army Medical Research Institute of Infectious Diseases at Fort Detrick, Md., injected small groups of cynomolgus macaques -- small, tree-dwelling monkeys -- with the vaccine for either Ebola or Marburg. Four weeks later, they were infected with one of the viruses.

None of the vaccinated monkeys died, nor did any become ill or suffer significant side effects.

Substantial Protection After Infection

"Any kind of vaccine for either one of these agents is exciting if it protects against a respectable challenge. And that certainly was a respectable challenge," said Nancy K. Jaax, former chief of comparative pathology at Fort Detrick.

Jones said the experimental vaccines also showed promising results when given orally or as an aerosol to mice. Both forms would make administering the vaccine easier in areas with poor public health systems.

In unpublished experiments using mice, the vaccines also provided substantial protection when administered shortly after infection, Jones said.