The unprecedented spread of the highly pathogenic avian influenza type A H5N1 is a threat to veterinary public health. However, the virus does not in its present form constitute a major threat to human public health. Only if the virus mutates to spread effectively from person to person will there be a risk of a new pandemic. It is not possible to predict if this will happen, when it may happen or how serious it may be. At present, seasonal influenza represents the greatest burden of illness among the three types of influenza A illness: seasonal, avian, and pandemic influenza.