A vaccine that protects monkeys against the highly deadly Marburg virus, a relative of Ebola, may also provide the first known treatment for the infection, researchers said.
Now they hope to use a similar vaccine to try to treat Ebola.
Both viruses have caused rare, but frightening and deadly, outbreaks in Africa and both are considered to be potential bioterror agents.
The vaccine was created using a harmless virus known as vesicular stomatitis virus, or VSV. The researchers took out one gene and replaced it with a key gene from Marburg virus.
When they infected monkeys with Marburg and then administered the vaccine, the monkeys were protected and stayed healthy, said Thomas Geisbert of the US Army Medical Research Institute of Infectious Diseases.
Unvaccinated monkeys died within 10 to 12 days.
"We were very surprised," Mr Geisbert said today.
Mr Geisbert, whose team worked with colleagues at the National Microbiology Laboratory at the Public Health Agency of Canada, published the findings in this week's issue of the Lancet medical journal.
He said it may be a while before the vaccine is tested in people but hopes it is a first step.
Marburg virus killed more than 300 people - 90 per cent of those infected - in Angola last year. Ebola is usually somewhat less deadly and killed 254 people between 2001 and 2005 in Gabon and the Democratic Republic of Congo.
There is no cure for either diseases, both caused by a family of viruses known as filoviruses. They lead to a particularly nasty form of haemorrhagic fever and victims usually die of multiple organ failure and shock.