An experimental nasal immunization for the respiratory illness SARS has proven effective in a test on monkeys, suggesting that a vaccine for humans might be most effectively delivered through the nose.
A study published Friday in The Lancet medical journal found that four African green monkeys given a single dose of the vaccine and then infected four weeks later with the severe acute respiratory syndrome virus developed neutralizing antibodies and showed no sign of the disease in their respiratory tracts.
Four monkeys in a control group that did not receive the vaccine _ created by inserting a protein from the SARS virus into a modified parainfluenza virus _ developed signs of "viral shedding," which indicates the presence of the SARS coronavirus.
The researchers from the U.S. National Institute of Allergy and Infectious Diseases in Bethesda, Md., said the results were "a very significant advance."
"We found that immunization with this single protein alone was enough to stimulate protection, and we showed it in monkeys," said Dr. Peter Collins, one of the report's authors.
"It seems we can fairly readily get a very strong immune response (to the SARS virus). I think a SARS vaccine will be achieved in the very near future."
Scientists from the institute have reported promising results from tests of two other potential vaccines on rodents, but this is the first they have tested on monkeys, which are genetically closer to human beings.
SARS has infected more than 8,000 people and killed more than 770 around the world since it being identified in China in 2002. Last month, scientists in China injected four volunteers with another experimental SARS vaccine, the first such trials on humans.
In the Lancet study, a live attenuated parainfluenza vaccine _ a weakened version of a virus responsible for respiratory infections like pneumonia _ was genetically modified with protein from the SARS virus in a bid to provoke an immune response.
Collins said the vaccine would be more effective on infants and children than on adults, who are likely to have built up an immunity to the parainfluenza virus through childhood illness. Researchers were looking for another virus that would be a suitable base for an adult vaccine before conducting clinical trials on humans, he said.
Although the number of animals tested in the Lancet study was small, the researchers said it illustrated the potential of directly immunizing the human respiratory tract, the main site of SARS transmission and disease.
"I think this is a route that will be used more and more for respiratory illnesses," Collins said. "That's where the virus replicates."
Earl Brown, a professor of virology at the University of Ottawa in Canada who was not connected to the study, said the test vaccine was encouraging.
"It's a very good step," he said. "It looks like an excellent candidate, but the safety issues have not been addressed yet."
Scientists are cautious with vaccines because of the risk they can trigger an off-kilter immune reaction, making the patient even sicker. A vaccine for the feline coronavirus _ a virus in the same family as SARS _ makes cats sicker when they catch the virus.
