In the past, influenza pandemics have been occurring every 20 to 30 years. Highly pathogenic avian influenza A(H5N1) has been causing unprecedented global outbreaks since 2003 and many human cases with a high case fatality rate have also been reported. But the virus that caused a pandemic in 2009 was A(H1N1) that was originated from swine influenza. The same subtype, A(H1N1) has been circulating in human population since 1977. This pandemic (H1N1) 2009 is also not as virulent as A(H5N1) in humans. Many aspects of pandemic (H1N1) 2009 are different from what we had been expecting. We should reconsider the concepts and the strategies for influenza pandemic by reviewing current pandemic (H1N1).
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