An influenza pandemic seems inevitable. The H5N1 influenza virus, known as the avian influenza, is currently circulating in Asia and has appeared in other regions. Avian influenza (flu), which has been transmitted from birds to humans on a limited basis, can be rapidly fatal, with a reported death rate of at least 50% in the documented human cases to date. If a human-to-human transmissible form emerges and spreads rapidly, it will pose a great threat to global public health, although the mortality rate may not be as high as that observed thus far. While various factors suggest that this strain could be the cause of the next pandemic, it is unknown when it will occur, whether it will be caused by H5N1 or another new virus or how severe it will be.