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Over the past couple of years Japan has emerged as one of the world’s most proactive nations when it comes to pandemic preparedness.
Last September roughly 6,000 medical workers received an experimental prepandemic vaccine, and this year it is anticipated that more than a million more may do the same (see Japan: Pre-Pandemic Vaccination Priority List).
The problem with prepandemic vaccines, of course, is that unless the prepandemic strain is reasonably close to the pandemic strain that emerges, it may not have much protective effect.
Scientists in Japan believe that a combination of different prepandemic vaccines, given some time apart, might provide for a wider immune response.
The hope is not so much that this would prevent a future infection from a pandemic strain, but that it would attenuate the symptoms and thereby reduce morbidity and mortality.
This report from the Mainichi Daily Times.
2 vaccines can stop new flu from becoming serious
(Mainichi Japan) April 7, 2009
The injection of two of three anti-flu vaccines at certain intervals, which have been developed in preparation for an outbreak of a new type of flu, are effective in preventing flu symptoms from becoming serious, a Health, Labor and Welfare Ministry research team said.
The research team made the discovery after conducting clinical tests on three types of pre-pandemic vaccines that it has made from the highly-virulent bird flu virus H5N1.
The ministry will determine the best method and timing for the vaccinations by the end of this year, ministry officials said.
In the clinical tests, 210 test subjects were inoculated with a vaccine based on a virus strain that a human was infected with from a bird in Vietnam, according to National Mie Hospital Director Toshiaki Ihara, who leads the research team. Three years later, they received an injection of either of the two other types of vaccine made from virus strains obtained in Indonesia and China.
It has turned out that about 67 to 96 percent of the test subjects became immune to the other type of virus, against which they were not vaccinated, three weeks after the second injection.
Moreover, it has proven that an additional vaccination helped improve the immunity of those who had received prior vaccinations only one week later.
"If the genotype of the vaccine is similar to that of a new type of flu, prior vaccination will likely be effective in preventing those who are infected from becoming seriously ill or dying," Ihara said.
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