Avian and pandemic influenza: an overview.

Influenza A/H5N1 (avian influenza) has now caused 258 human infections (as of November 13, 2006), with an approximate 50% mortality rate. Because the virus is novel in terms of antigenic type and causes infection and illness, and because humans have no pre-existing immunity, the conditions for a possible pandemic exist. Additionally, wild migratory birds appear to be spreading the virus across ever larger geographic areas, and newer clade 2 influenza A/H5N1 viruses have begun to emerge. The US Congressional Budget Office has formally modeled the likely consequences of pandemic influenza and estimates that up to 2 million of the US population might die, with up to 40% of all workers ill for as long as 3 or more weeks. This brief overview will review basic virologic, immunologic and epidemiologic information relevant to understanding and preparing for this threat. In particular, the role of avian influenza vaccines will be reviewed.