Researchers at the University of Pittsburgh said that they have genetically engineered an avian flu vaccine. The vaccine contains the components of the deadly strain H5N1.
This vaccine in animal models offered complete protection to mice and chickens from infection. The vaccine contains a live virus, which is very efficient in producing an immune response than those prepared by traditional methods. It is cultured in cells and very easily produced in large amounts. It prevents the spread of the virus in domestic livestock populations and humans. The findings were published in the Journal of Virology.
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 said that the vaccine stimulates several lines of immunity against H5N1.
Dr. Gambotto and his colleagues genetically engineering a common cold virus (adenovirus) to express the avian influenza protein (hemagglutinin) (HA) on its surface. This virus then attaches to all the cells that are infected. Bird flu (H5N1) has affected a large number of birds in different areas like Cambodia, China, Indonesia, Japan, Laos, South Korea, Thailand and Vietnam, Turkey and Romania. Due to this 150 to 200 million birds have been culled to prevent the spread of infection.
The first incidence of bird flu attack in humans was in 1997 at Hong Kong. The virus causes severe respiratory illness resulting in death.
The adenovirus serves as vector or transporting vehicle for delivering the foreign genes or DNA of the HA protein.
Dr. Gambotto's team took two sets of mice in one set they injected the genetically engineered vaccine and in the other an adenovirus vector containing no H5N1 genes, or an empty vector. The mice immunized with the empty vector showed substantial weight loss and all were dead within six to nine days of avian flu exposure. On the other hand, most of the mice immunized with the adenovirus containing the HA protein showed only mild weight loss and survived H5N1 infection. It was also found that full length HA vaccine gave a complete protection against the H5N1 strain.
The mice which is immunized with full-length HA vaccine developed strong T-cell responses. Hence this recombinant vaccine offers a greater therapeutic value. Even if H5N1 mutates, the vaccine is still offers protection against the disease.
Based on the superior degree of protection that they found in mice vaccinated with full-length HA vaccine, Dr. Gambotto's group along with David E. Swayne, D.V.M., Ph.D., at the U.S. Department of Agriculture, tested the vaccine's effectiveness in chickens. Chickens were injected with the vaccine and the empty vector both intranasally and subcutaneously. The chickens were then challenged with a dose of whole H5N1 virus 10,000 times greater than the dose given to the mice.
It was found that all of the chickens that were immunized subcutaneously survived exposure to H5N1 and developed strong HA-specific antibody responses and showed no clinical signs of disease. On the other hand 50% of those that were immunized intranasally died. All of the chickens immunized with the empty vector (intranasally and subcutaneously) died within two days of H5N1 exposure.
Dr. Gambotto and his colleagues suggest that these live vaccines can be used in combination with the traditional inactivated influenza vaccines.
Hence the research team concludes by saying that the new vaccine would have the ability to contain outbreaks of mutant strains. Further trails in the humans have to be conducted in order to understand the efficiency of the vaccine in humans.