Bird Flu Vaccine Proves Successful

The success of a commercially produced vaccine in protecting laboratory animals from bird flu virus during studies performed at St. Jude suggests that it would protect humans if the virus mutates and acquires the ability to spread from person to person.

Researchers at St. Jude Children’s Research Hospital said they have taken a significant step in the development of a vaccine that could protect humans against a bird flu virus if it mutates into a form that can be passed from person to person.The investigators announced they had protected mice and ferrets against a highly lethal avian influenza virus using a commercially developed DNA-based vaccine that was previously shown to protect animals against multiple human flu strains. The vaccine’s ability to protect against both human flu viruses and H5N1 – the bird flu virus -suggests that such a vaccine could protect humans if an H5N1 virus mutates so that it can pass easily from person to person, according to Richard Webby, PhD, assistant member of Infectious Diseases at St. Jude.These findings are important because international research and public health officials fear that if H5N1 adapts to humans and permits person-to-person transmission, a resulting pandemic (worldwide epidemic) could kill many tens of millions of people and cause severe economic damage to countries.The vaccine was developed by Vical Inc. of San Diego, California, using their patented technology. Webby presented the findings of this study at the U.S. Public Health Service Professional Conference in Denver, Colorado, May 3.”Our expertise in this area of H5N1 vaccine research is what prompted Vical to invite us to join them in this important work,” Webby said. Webby is the subcontractor for Vical on a grant from the National Institute of Allergies and Infectious Diseases to study this vaccine. If H5N1 mutates and becomes fully adapted to humans, health officials will benefit by having access to a number of different options for vaccines and antiviral agents, according to Webby. “This DNA-based vaccine overcomes some technical problems that slow production of conventional vaccines and reduces their ability to protect against viruses that mutate,” Webby said. The investigators used two versions of Vical’s multi-component, DNA-based vaccine in the studies. One vaccine was directed against three viral proteins: NP and M2, which are “conserved” proteins that generally do not mutate quickly and therefore are slow to avoid immune responses triggered by the vaccine; and H5, a “variable” protein on the surface of the bird and human flu viruses that is critical to their ability to infect cells. This variable protein is known to mutate readily, thereby foiling previous immune responses it triggered – whether due to natural exposure or vaccination. The other version of the vaccine contained only the two conserved viral proteins.In the St. Jude study, the full, three-component vaccine (H5, NP and M2) provided complete protection in mice against lethal challenges with a highly virulent (Vietnam/1203/2004) H5N1 avian influenza virus. Moreover, previous studies showed that a smaller version of the vaccine containing only the NP and M2 components provided significant protection against several strains of human influenza virus as well as the H5N1 “bird flu” strain.”Such cross-protection against bird and human influenza is considered by researchers to be the ‘Holy Grail’ of flu vaccines,” noted Webby. “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.””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,” Webby said. “We wouldn’t have to wait to start developing a vaccine against it until after the original virus mutated.”Vical made the vaccine by inserting the gene for each protein into a separate plasmid – a small circular piece of DNA normally found in bacteria. Each plasmid was inserted into different bacteria (Escherichia coli) and the bacteria grown into large numbers in a fermentation vat. As the bacteria multiplied they copied the plasmids containing each gene. The genes were then extracted and combined in a solution with another ingredient designed to increase the ability of the vaccine to stimulate the immune system.Neither Webby nor the other members of the St. Jude team own stock in Vical or have any financial interest in this project.(Source: St. Jude Children’s Research Hospital: May 2006.)