Based on the superior degree of protection that they found in mice vaccinated with full-length HA vaccine, Dr. Gambotto's group, working with David E. Swayne, D.V.M., Ph.D., at the U.S. Department of Agriculture, tested its effectiveness in chickens, which have almost a 100 percent mortality rate to H5N1 exposure. In all, the researchers inoculated four groups of chickens either through their noses (intranasally) or with subcutaneous injections of either the HA-containing vaccine or the empty vector vaccine. The chickens were then challenged with a dose of whole H5N1 virus 10,000 times greater than the dose given to the mice and significantly greater than the dose farm chickens are likely to be exposed to during a natural outbreak.
Interestingly, all of the chickens that were immunized subcutaneously survived exposure to H5N1, developed strong HA-specific antibody responses and showed no clinical signs of disease. In contrast, half of the chickens immunized intranasally died and half survived. All of the chickens immunized with the empty vector (intranasally and subcutaneously) died within two days of H5N1 exposure. The researchers are still not yet sure why the subcutaneous delivery is more effective than the intranasal delivery of the vaccine, but they suggested it may be because the adenovirus vector they used has limited infectivity via the nose and respiratory tract.
Dr. Gambotto and his colleagues suggest that rather than replacing traditional inactivated influenza vaccines, their adenovirus-based vaccine could be a critically important complement to them. Because it appears to be so successful in immunizing chickens against H5N1, widespread inoculation of susceptible poultry populations could provide a significant barrier to the spread of the virus via that route in this country and other countries that have so far been spared from avian flu. Also, if there were a dis
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26-Jan-2006