This research study is being done because influenza (flu) affects many people each year throughout the world. The elderly and those with chronic health problems are at greater risk for complications from the flu. The purpose of this research study is to evaluate vaccination strategies in the elderly and others receiving the influenza vaccination in order to increase protection. All subjects will receive the flu vaccine as an injection in the muscle of the upper arm. Participants may receive a booster [an extra dose of vaccine or placebo (inactive substance)] shot. Study participants will include healthy adult volunteers, ages 21-40, 60-89, or 90 years and older. Subjects will be involved in study related procedures for 6 months.