The history of pandemic influenza, along with the evolving epizootic of the highly pathogenic avian influenza A (H5N1) virus and the severity of associated human infections, serve as a warning to the world of the threat of another influenza pandemic. Conservative estimates suggest that up to 350 million people could die and many more would be affected, causing disruption to health-care systems, society, and the world's economy. WHO has encouraged countries to prepare in advance by developing influenza pandemic preparedness plans that involve public-health and pharmaceutical interventions. Vaccination is a cornerstone of these plans; however, a pandemic vaccine cannot be manufactured in advance because the next pandemic virus cannot be predicted. The concepts of vaccine stockpiling and prepandemic vaccination have thus become attractive. Human H5N1 vaccines are currently available and can induce heterotypic immunity. WHO and governments should give urgent consideration to the use of these vaccines for the priming of individuals or communities who would be at greatest risk of infection if an H5N1 influenza pandemic were to emerge.