Potential target populations for RSV vaccines include 1) pregnant women, 2) infants <6 months of age, 3) infants and children >6 months to 2 years, 4) young (2–5 years old) and school-age children, and 5) individuals >60 years of age. Children less than 2 years of age and the elderly would derive the most direct benefit from an effective vaccine. Since all children are infected early in life, anyone over 2 years of age is likely to have experienced natural infection, so vaccination of older children and adults is designed to boost pre-existing immunity. Vaccination in children under 2 years of age could be the primary immunization event.