WEDNESDAY, Feb. 1, 2006 (HealthDay News) -- Scientists have succeeded in creating a genetically engineered vaccine that protects mice from several different strains of the deadly H5N1 bird flu virus.
Experts hope the same vaccine or a similar one will one day work in humans, according to the study, which appears in the Feb. 2 issue of The Lancet.
The vaccine uses a common-cold virus, meaning it can be quickly and easily produced and, because it is active against different virus strains, can also be stockpiled for use in a future pandemic, the researchers said.
"This is an exciting accomplishment," said Dr. Marc Siegel, clinical associate professor of medicine at New York University School of Medicine and author of Bird Flu: Everything You Need to Know About the Next Pandemic. "It bodes well for the future upgrade of our current method of making all flu vaccines for humans."
"There are two main advantages," added Dr. Leon Russell, president of the World Veterinary Association and a professor of veterinary integrative biosciences at Texas A&M College of Veterinary Medicine. "You don't have to use eggs and it's just one strain, kind of a blanket strain, so it would be much more efficient. That's very important."
The current human flu vaccine given annually contains three strains. Its
production system is based on chicken-egg technology. The system is cumbersome, requiring millions of fertilized chicken eggs and taking at least six months -- too long to protect billions of people against a pandemic.
And the need to protect humans from bird, or avian, flu is gaining greater urgency. Bird influenza has become endemic in domestic poultry in Southeast Asia. The virus has also skipped to dozens of humans. Since January 2004, at least 152 laboratory-confirmed cases of human infection have been reported to the World Health Organization, and 85 people have died from the disease.
So far, however, the virus appears to lack the ability to jump easily from human to human, exactly the capability it needs to ignite a pandemic.
Earlier this week, researchers at the University of Pittsburgh reported success with a genetically engineered bird flu vaccine that protected mice and chickens.
For the new study, researchers from Purdue University and the U.S. Centers for Disease Control and Prevention used a genetically engineered adenovirus (a common cold virus) to produce hemagglutinin subtype 5 (H5HA), a protein that is a component of the H5N1 virus. The protein was isolated from a human case of bird flu in Hong Kong occurring in 1997.
"Our approach did away with the egg," said Dr. Suresh Mittal, co-author of the paper and a professor of virology at Purdue University in West Lafayette, Ind.
The new vaccine is also not solely dependent on an antibody response.
"Traditional vaccines base their protection on the antibodies they produce against the virus, but the antibodies only protect against very, very similar strains," Mittal explained. "They don't have the capacity of covering strains if they mutate."
A cellular immune response -- in which the immune system mounts a response that can recognize virus-infected cells and then destroy those cells -- would be more powerful.
It also means the vaccine could be more easily stockpiled because a version made today would still be effective in the future.
Mittal's team injected one group of lab mice with the new vaccine and another control group with saline, or a salt water solution.
All of the mice were then infected with the 1997 virus as well as a strain from 2003 and one from 2004.
Despite low antibody response, "all the mice were protected" against all strains of the virus, Mittal reported. "It's showing that even though the vaccine was against an older virus, it can still protect against some of the newly isolated viruses."
One possible drawback, Russell said, is that the vaccine had to be given twice, four weeks apart. "That always presents problems, trying to get people coming in twice," he added.
The vaccine needs to be tested on humans, but Mittal is optimistic.
"The common cold virus has been used in humans for gene therapy so that gives us some clue that these vaccines will work," he said. "But we have to do some human studies before we know how they will work."
Humans will be given the vaccine but not the virus. Instead, the effectiveness of the vaccine will be assessed by looking at antibody and cellular immune responses.
Human studies will also determine if there are any adverse reactions.
Still, progress is likely to be slow.
"Whenever we go to a new technology, there are some cautious steps that should be taken," Mittal said. "More studies have to be done in animals as well as in humans before the scientific community and the public in general have more faith in these newer approaches."
More information
The World Health Organization has more on avian flu.
