[New pandemic influenza: what are the risks?]

Influenza pandemics result from the introduction of a new influenza A subtype from the avian reservoir. This reservoir is vast but the introductions are seldom. To be adapted for human infection, they have to undergo major changes. Two mechanisms have been described, allowing this adaptation: direct adaptation after accumulation of mutations, or genetic exchange between human and avian viruses (reassortant virus). Today, we are facing a pandemic threat due to A(H5N1). Already 382 cases have been detected, including 241 death cases. However, this virus is not adapted to man. On the other hand, the large epizootic clusters observed, the cases observed after exposition to infected poultry and the lack of control of the A(H5N1) infection in wild and domestic birds make this virus the best candidate for the next pandemic.