Vaccine protects monkeys from Ebola virus.

Using a double-barreled approach to immunization, scientists have created a combination of vaccines that fends off deadly Ebola virus in monkeys. The new inoculation uses pieces of Ebola DNA both by themselves and in an adenovirus, a virus commonly modified to carry genes.

"This is a good first step," says Paul W. H.I. Parren, an immunologist at the Scripps Research Institute in La Jolla, Calif. It's the first published success in immunizing primates against Ebola, he says.

The vaccine needs more testing before it can be tried in people, says study coauthor Gary J. Nabel, director of the Vaccine Research Center at the National Institutes of Health in Bethesda, Md. But once an Ebola vaccine proves safe for people, he says, health organizations might first give it to workers sent to contain outbreaks--a dangerous job. A reliable vaccine would also provide some peace of mind to researchers, who wear full-body suits when working with the virus in laboratories, Nabel says.

However, a broad vaccination campaign would be difficult, Parren says, because Ebola's natural reservoir in the wild remains unknown and the disease strikes unexpectedly.

To test the immunization strategy, researchers injected each of four cynomolgous macaques with three doses of the DNA-only vaccine over 2 months. Twelve weeks later, each monkey received a single injection of the adenovirus vaccine. Four other macaques received blank injections. Later, the researchers exposed all eight animals to Ebola.

Within a week, the four untreated monkeys were dead. The four vaccinated monkeys survived the virus and were still healthy 6 months later, Nabel says. The study appears in the Nov. 30 NATURE.

Ebola comes in three strains, dubbed Zaire, Sudan, and Ivory Coast. Ebola Zaire is named for the country, now called the Democratic Republic of Congo (DRC), where health workers first detected the disease in 1976. In the new study, the scientists exposed the monkeys to Ebola Zaire. The researchers will probably next test the vaccine combination against Ebola Sudan, Nabel says.

In earlier experiments, a similar DNA vaccine protected rodents (SN: 1/10/98, p. 22). The DNA vaccine in the new study contains a mix of genes that encode surface glycoproteins found on each of the three Ebola viral strains. The adenovirus carries a gene encoding an Ebola Zaire glycoprotein.

The DNA vaccine seemed to prime the immune system modestly, and the adenovirus vaccine "gave it an extra kick, boosting antibody levels," Nabel says.

Ebola causes flulike symptoms and severe internal bleeding. There is no treatment, and the disease spreads easily through human contact--even a handshake. The Zaire and Sudan strains kill 90 percent of their victims, but the Ivory Coast strain is much less dangerous.