An experimental SARS vaccine protected mice against the respiratory illness that killed nearly 800 people worldwide last year, but a safe and effective vaccine for humans is probably still a long way off.
Results published in Thursday's issue of the journal Nature show the vaccine triggered an immune response in the mice and dramatically reduced the level of the virus in the lungs of inoculated mice.
But researchers at the National Institute of Allergy and Infectious Diseases, which developed the gene-based vaccine, said more experiments are needed to determine if it will work in humans.
Scientists not involved in the study called the results promising, but noted that DNA vaccines have not yet been shown to effectively treat any viral disease, and the approach is still unproven compared to conventional vaccines.
"I don't think it's a home run," said Dr. Robert Brunham, director of the University of British Columbia Centre for Disease Control in Canada.
Canada's tourism industry was devastated last year after more than 40 people in the Toronto area died from SARS infection. The SARS outbreak sickened more than 8,000 people worldwide, and at least 774 died.
SARS, or severe acute respiratory syndrome, emerged in southern China in late 2002 and spread to more than two dozen countries on four continents before it was contained last summer.
Earlier this year, China approved plans to test an experimental SARS vaccine in human clinical trials. The vaccine, made from a dead virus, had been shown to work in animals.
Vaccines are normally made from killed or weakened viruses and work by mobilizing the body's immune system to build defenses by showing it what the targeted virus looks like. That approach is used every year to develop flu shots to combat emerging strains of influenza.
But the SARS vaccine was made from a small piece of genetic material from the virus called a plasmid. It biochemically locks onto a specific protein on the outer surface of the virus. This alerts the body's immune system to launch a counterattack against the invading virus.
Scientists tested two versions of the DNA vaccine in 15 mice over a six-week period. The vaccines differed in how much genetic material scientists removed from the original piece of DNA. Both worked, although one appeared to be more effective than the other.
Dr. Gary Nabel, chief of the NIH Vaccine Research Center and the study's lead author, said the government is working with San Diego-based Vical Inc. to make a purified vaccine for human testing pending approval from the Food and Drug Administration.
Last May, two research teams separately published the genetic sequences of the SARS virus in an effort to find drugs to treat SARS or develop a vaccine to prevent it.
Civet cats and other mongoose-like animals that are sold in live food markets in southern China are suspected of spreading SARS to humans, although the original source of the virus has not been determined.
On the Net: Nature journal: www.nature.com
Vaccine Research Center: www.niaid.nih.gov/vrc