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| |  Booster Shot May Help Control Future Avian Influenza Pandemic CHICAGO -- July 17, 2008 -- A booster vaccination against H5N1 avian influenza given years after initial vaccination, with a different strain, may prove useful in controlling a potential future pandemic, according to a study published in the August 1 issue of The Journal of Infectious Diseases. H5N1 avian influenza continues to pose a major health risk to birds and humans. As of mid-June, more than 60% of the more than 380 human cases have been fatal, and hundreds of millions of birds have died or been culled to prevent the spread of the disease. This new study is the first to report that giving 1 dose of a newer-clade vaccine to those who were vaccinated previously with older versions is more effective than giving only doses of the newer vaccine to unvaccinated subjects. Nega Ali Goji, MD, University of Rochester Medical Center, Rochester, New York, and colleagues gave a single booster dose of a vaccine based on a clade 1 H5N1 virus circulating in Vietnam in 2004 to subjects who 8 years earlier had received 2 doses of a vaccine based on the original, clade 0 virus that appeared in Hong Kong in 1997. Sixty-four percent had a positive immune response, which compares favourably with the results of a previous study using 2 doses of the clade 1 Vietnam virus, in which only 43% of those vaccinated had a positive immune response. The results not only support the booster technique but also show that even though the virus had mutated since the initial vaccination, using it to boost an earlier vaccine is more effective than simply vaccinating subjects with the most current vaccine. "These results suggest that one strategy for pandemic control could involve prevaccination of some segments of the population prior to the emergence of a pandemic, so that effective protection could be achieved with a single dose schedule if and when a pandemic emerges," the authors wrote. "If the finding that priming can result in enhanced responses to single-dose vaccination schedules were confirmed, then prepandemic vaccination programs could be considered, especially in populations of first responders, healthcare workers, or the military. Such populations might then be able to be effectively and rapidly vaccinated with a single dose of a vaccine specific for an emerging pandemic, if it were to occur."
SOURCE: Infectious Diseases Society of America
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