A single shot of a new vaccine against the Ebola virus offers fast and apparently solid protection in monkeys, scientists report in a paper published in the 7 August issue of Nature. The vaccine could be particularly useful during outbreaks, when a rapid response is crucial, the researchers say.
Three years ago, Gary Nabel and his colleagues at the Vaccine Research Center of the U.S. National Institute of Allergy and Infectious Diseases first reported that they could protect monkeys from a deadly dose of Ebola using a two-pronged vaccine. First, they gave three injections--each 4 weeks apart--with a piece of "naked DNA" encoding the Ebola surface glycoprotein. That was followed, 3 months later, with a live adenovirus engineered to produce the same protein (ScienceNOW, 29 November 2000). The approach, currently fashionable in vaccine research, was aimed at producing as robust an immune defense as possible. "We basically pulled out the heavy artillery," Nabel says.
Now, the same team has found that lighter arms can do the job too--and faster. First, they dropped the DNA shots, but they injected the modified adenovirus twice, 9 weeks apart. When this turned out to protect monkeys just as well, the team skipped the second adenovirus shot too and infected eight monkeys with Ebola--four of them with a very high dose--a mere 4 weeks after vaccinating them. All eight survived, whereas controls all died.
"I'm impressed," says immunologist Dennis Burton of the Scripps Research Institute in La Jolla, California. "This is very encouraging." What's more, he adds, the higher Ebola dose takes care of concerns--expressed by Burton and others--that the challenge dose used in the 2000 study was low comparable to what humans can be exposed to. "That criticism evaporates," Burton says.
Nabel says both vaccines will undergo further testing and human trials. The dual vaccine produces a stronger immune response and may well offer longer-lasting protection, he says, so perhaps it's preferable for vaccinating, say, health care workers or scientists who might come into contact with the virus. But the single adenovirus shot could be useful when every day counts; Nabel says it might be used to contain an outbreak using ring vaccination, the strategy that helped eradicate smallpox.