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Over the past few years the world has produced a few dozen million doses of various pre-pandemic H5N1 vaccines. A handful of countries have small stockpiles, and a few, like Switzerland, reportedly have enough to inoculate their entire nation.
As these vaccines are all based on older clades of the H5N1 bird flu virus, how effective they would be against a mutated strain is largely unknown.
The problem is that these vaccines have a limited shelf life - normally somewhere between 18 months and 2 years. Over the next year it is likely that millions of doses will expire.
With the prospect of `using them, or losing them' looming large, the idea of early administration of them to essential workers is now under consideration. Japan is one country currently considering that option.
Influenza vaccines generally produce the highest immune responses during the first 5 or 6 months after administration, then gradually lose their effectiveness. The concern is that giving the vaccine too early would result in greatly reduced protection if and when a pandemic were to erupt.
New research, published in the August edition of The Journal of Infectious Diseases , appears to bolster hopes that early administration of a prepandemic vaccine can prime the recipient for a later vaccine.
Subjects who received an early, experimental vaccine, eight years ago in Hong Kong were given a single booster shot of a clade 1 H5N1 vaccine.
Normally it takes two shots over a 30 day time span to achieve an acceptable immune response. In this case, a single `booster shot' produced an encouraging 64% immune response.
Exactly how effective this strategy would be under real pandemic conditions is unknown, but it does lend support to the idea that soon-to-expire vaccines could be `stored in people', instead of being disposed of when they reach the end of their shelf life.
These snippets come from a press release by the Infectious Disease Society of America.
Booster vaccination may help with possible future avian influenza pandemic
New evidence suggests that 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. The study is published in the August 1 issue of The Journal of Infectious Diseases, now available online.
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The study, conducted by Nega Ali Goji, MD, and colleagues from New York, Maryland, and Alabama, gave a single booster dose of a vaccine based on a clade 1 H5N1 virus circulating in Vietnam in 2004 to subjects who eight years earlier had received two 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 favorably to the results of a previous study using two doses of the clade 1 Vietnam virus, in which only 43 percent 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 findings are important given the fact that influenza viruses are mutating constantly.
<snip>
In an accompanying editorial, Gregory A. Poland, MD, of the Mayo Clinic College of Medicine, noted that some are already looking to begin such prevaccination primers against H5N1 influenza. For example, Japan is planning to immunize health care workers starting in 2009, and the U.S. Department of Defense is offering a vaccine to those in high risk specialties.
Dr. Poland pointed out that new studies are needed to investigate different types of vaccine administration, deal with vaccinations that prevent death but not infection and illness, search for more broadly cross-protective influenza vaccines, and collect data on the vaccination of those who are not healthy adults.
Although, he said, "determining who should receive these vaccines, when, and in what order and under what circumstances deserves widespread debate," he agrees that the findings of the study are novel, as they "suggest that such a prime-boost strategy using vaccines derived from different H5 clades, separated by years, may be worthwhile, immunologically feasible, and safe."
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