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Although influenza A/H1N1pdm09 is not causing a pandemic anymore, we recently observed two critically ill pregnant women infected by this virus. We present these cases to illustrate the possible severe complications of an – at that moment – seasonal influenza in pregnancy. We discuss the epidemiological differences between the pandemic and postpandemic phase and try to explain the high virulence of H1N1-infections in pregnancy by discussing insights in immunology during pregnancy. We conclude that although the influenza A/H1N1pdm09 is in the postpandemic phase, infection by this influenza virus still needs to be considered in pregnant women with progressive respiratory dysfunction.
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