LONDON — A new vaccine that protects monkeys against the deadly Ebola virus could lead to the development of a similar one for humans, scientists said Wednesday.
Ebola is a disease that causes high fever, massive internal bleeding and death usually within seven to 21 days of infection. It strikes quickly and unexpectedly and kills 90 percent of its victims. Hundreds of people have died in recent outbreaks.
A team of scientists, led by researchers at the National Institutes of Health (NIH), has successfully vaccinated four monkeys against what would be a lethal dose of the virus.
"We don't know if this model perfectly replicates what happens in humans. It remains an open question whether this vaccine strategy will be successful in humans," Gary Nabel, of the Dale and Betty Bumpers Vaccine Research Center at the NIH, said in a telephone interview.
"It will serve as a model to give us the scientific information that we need to learn how to develop the vaccine," he said.
The vaccine uses strains of DNA containing genes that encode Ebola virus proteins to induce an immune response. The researchers also boosted that response by including a weakened strain of a different virus in the vaccine.
Nabel and his team, whose research is published in the science journal Nature, said the four monkeys injected with the vaccine were protected from the virus and were still free of infection six months later.
"Ebola is a difficult virus because currently available antiviral drugs have no proven effect on it, and we do not know its natural reservoir, making environmental control impossible," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases at the NIH.
"A vaccine is therefore the best hope for protecting humans from infection, and this study makes some key advances toward realizing that goal," he said.
A human vaccine will have to protect against the three known fatal Ebola strains — Zaire, Sudan and Ivory Coast.
The vaccine tested on the monkeys includes genes encoding proteins from the three strains of the virus.
"We of course want to test the multivalent vaccine for effectiveness against all three strains of Ebola, but we also need to look more closely at the immune response induced by these vaccines so we can nail down what is needed for protection," said Dr. Nancy Sullivan, who worked on the project.
The Ebola virus was first identified in 1976. It emerged from an unknown source, which scientists suspect was an animal, and caused outbreaks in Sudan and the former Zaire, now the Democratic Republic of the Congo.
Isolated outbreaks have occurred since, most recently in Uganda where the Sudan strain had killed 129 people as of Nov.24.
The virus is extremely infectious and spread through direct physical contact. It can be transmitted through a handshake, coughing or sneezing.
"Time will tell whether this is a vaccine that has success in people. The results of the study encourage us to pursue this as a vaccine candidate in humans," Nabel said.