Safety and Immunogenicity of ChimeriVax-WN02 West Nile Vaccine in Healthy Adults

West Nile Disease has been carried across the United States by migrating birds since it was first identified in New York city in 1999. It is transmitted by mosquitoes from birds to humans and can cause severe disease in some individuals. There is no specific treatment for West Nile Disease. The target population for a West Nile vaccine is older people, as they are more susceptible to severe disease. This trial includes a dose-finding part with a placebo control in young healthy adults, followed by a placebo-controlled examination of the chosen dose in older healthy adults. Outcome measures include a comparison of adverse events between active treatment and placebo, a comparison of antibody and viremia measurements between dose levels and across age groups for the dose chosen for Part 2.