Researchers from the University of Pittsburgh have designed a vaccine that successfully fought the bird flu virus in mice and chickens.
Findings from their collaboration with investigators at the Influenza Branch of the Centers for Disease Control and Prevention are in the Feb. 15 issue of the Journal of Virology, a publication of the Washington, D.C.-based American Society for Microbiology.
The researchers tested slightly different viruses that contained either the whole, part of or none of a bird flu protein called hemagglutinin (HA).
They injected mice with the viruses to see which offered protection from H5N1 infection. The mice were then inspected for any signs of illness (i.e., weight loss and death) and for antiviral antibodies and other immunity markers in their blood.
Most of the mice immunized with the virus containing either the whole or part of the HA protein showed only mild and short-lived weight loss, and they survived.
Those exposed to the common H5N1 virus died within six to nine days of exposure.
Researchers determined that the genetically engineered versions of the vaccine stimulated several lines of defense against the H5N1 virus, and they suggested that even if H5N1 mutates or changes its structure rapidly, the vaccine would still likely be effective.
There is one caveat, though. The researchers determined that the vaccines were only effective when delivered through the skin, not inhaled nasally. They aren’t sure why, but suggested that it may be because the virus they used had limited infectivity in the nose and respiratory tract.
After testing mice, the researchers moved onto chickens, where they tested a dose of the virus that was 10,000 times greater. They saw no signs of bird flu.
Researchers said these findings suggest that adding their vaccine to the traditionally inactivated flu vaccines in chickens could successfully render the bird flu harmless.
Flu vaccines currently are prepared in fertilized chicken eggs, a process developed more than 50 years ago that requires millions of eggs. The U.S. and the world would be in short supply of such a volume of eggs if a pandemic were to occur.
“Although the development of a vaccine for H5N1 in humans has been difficult, the recent study suggests it should be possible,” said Tony Mazzulli, M.D., of Mount Sinai Hospital Department of Microbiology in Toronto. “The overall process of producing the vaccine and ensuring that it not only works, but that it is also safe, may take some time.”
He added:”Although measuring a person’s antibody response following vaccination is a good way of determining if a vaccine can stimulate an immune response, it is impossible to know if the response will be protective against the wild type virus.”
Mazzulli said given the high death rate of H5N1, it will not be possible to determine by exposure if people are protected by the vaccine. “Even if the vaccine works initially, how will a person’s immune response protect them from infection?” he asked. “Will the response fade with time, in which case repeated vaccination will be needed – but at what frequency or at what intervals?”
The researchers are working on a small clinical trial of the vaccine in humans in the very near future.
Source: myDNA
