New Bird Flu Vaccine Proves Successful

MEMPHIS, Tennessee, May 3, 2006 (ENS) - A commercially developed vaccine funded by the U.S. National Institutes of Health has protected mice and ferrets against a deadly bird flu viral strain.

The success of the vaccine in protecting laboratory animals from bird flu virus during studies performed at St. Jude Children’s Research Hospital in Memphis suggests that it would protect humans if the virus mutates and acquires the ability to spread from person to person, according to the investigator who led the study.

The finding, coupled with results of previous studies that showed protection against multiple human influenza strains, suggests that such a vaccine would protect humans against multiple variants of the bird and human influenza viruses, said Richard Webby, PhD, assistant member of the faculty in the Department of Infectious Diseases at St. Jude.

Webby presented the findings of this study today at the U.S. Public Health Service Professional Conference in Denver, Colorado.

Virologist Dr. Richard Webby was successful in protecting mice and ferrets from the deadly bird flu. (Photo courtesy St. Jude)

Webby said, “Such cross-protection against bird and human influenza is considered by researchers to be the Holy Grail of flu vaccines."

The California company Vical Inc. developed the vaccine. "We are encouraged by the protection afforded by our avian flu vaccine and by the cross-protection data," said Vijay Samant, president and CEO of Vical.

"Achieving cross-protection is the ultimate goal in flu vaccines, and the current studies provide evidence that such a goal may be feasible using a DNA vaccine targeting conserved influenza virus proteins and formulated with our proprietary Vaxfectin adjuvant," said Samant.

The DNA based vaccine does not rely on chicken eggs or complex cell culture manufacturing methods. "DNA vaccines are manufactured by simple bacterial fermentation methods that may allow production of large quantities in a short period of time," said Samant.

The studies included 16 mice or six ferrets in each vaccine or control group, and the investigators used two versions of Vical's DNA-based vaccine in the studies.

One vaccine was directed against three viral proteins – NP, M2 and H5.

From left: Influenza virus specialist Dr. Robert Webster and Dr. Richard Webby, both of St. Jude, trace the evolution of the H5N1 virus in the lab. (Photo courtesy St. Jude)

H5 is a mutating protein on the surface of the bird and human flu viruses that is critical to the viruses’ ability to infect cells. The H5 protein easily mutates, so it can avoid immune responses triggered naturally or by a vaccine.

The other vaccine used in the study contained only the two conserved viral proteins, NP and M2.

All test DNA vaccines were formulated with the company's Vaxfectin adjuvant. An adjuvant is an additive administered with a vaccine that has little effect by itself, but improves the response of the immune system to the vaccine.

In the St. Jude study, the three-component vaccine (H5, NP, M2) protected the mice completely against potentially lethal challenges with a highly virulent H5N1 avian influenza virus.

Other studies showed that a version of the vaccine containing only the NP and M2 components provided significant protection against several strains of human influenza virus and the H5N1 bird flu strain.

“By stimulating immune responses against targets not likely to mutate, the vaccine could trigger an immune defense against a broad range of variants of the virus,” Webby explained.

“Even if the bird flu virus mutates so it becomes adapted to humans, this kind of cross protection will allow the immune system to track and attack such an emerging new variant without missing a beat,” he said. “We wouldn’t have to wait to start developing a vaccine against it until after the original virus mutated.”

In January, University of Pittsburgh scientists announced that they genetically engineered a bird flu vaccine from components of the deadly H5N1 virus that completely protected mice and chickens from infection. The vaccine can be made quickly and induced a strong immune response in the animals, making it a potentially useful tool for preventing the spread of the virus.

This vaccine contains a live virus, so it activates immune responses better than avian flu vaccines prepared by traditional methods, say the researchers. Because it is grown in cells, it can be produced much more quickly than traditional vaccines, according to the study, published in the February 15 issue of the "Journal of Virology."

“The results of this animal trial are very promising, not only because our vaccine completely protected animals that otherwise would have died, but also because we found that one form of the vaccine stimulates several lines of immunity against H5N1,” said Andrea Gambotto, M.D., assistant professor in the departments of surgery and molecular genetics and biochemistry, University of Pittsburgh School of Medicine, and lead author of the study.