Speaking at a Senate hearing Tuesday, scientists said that a vaccine to protect the elderly against the West Nile virus could be ready in about three years. According to Dr. Anthony Fauci, head of the National Institutes of Allergy and Infectious Diseases, an experimental vaccine in which West Nile genes were added to the structure of the yellow fever vaccine safeguarded animals against West Nile. Dr. Fauci noted that Acambis, a biotechnology company, plans to launch small human safety tests of the vaccine soon, and if it is found successful, the vaccine will likely be used during outbreaks to protect the elderly and those with weakened immune systems.