Safety and Immunogenicity of the RSV D46cpΔM2-2 Vaccine in RSV-Seropositive Children and RSV-Seronegative Infants and Children

Human RSV is the most common viral cause of serious acute lower respiratory illness (LRI) in infants and children under 5 years of age worldwide. This study will evaluate the safety and immunogenicity of the RSV D46cpΔM2-2 vaccine in RSV-seropositive children and RSV-seronegative infants and children. The vaccine will be evaluated in a stepwise fashion beginning in RSV-seropositive children (Group 1), and then in RSV-seronegative infants and children (Group 2). In each group, participants will be randomly assigned to receive a single dose of D46cpΔM2-2 vaccine or placebo at study entry (day 0). Participants will be enrolled in the study between April 1 and October 31, outside of the RSV season. Group 1 (RSV-seropositive children) will attend several study visits and will be followed for 28 days. Group 2 (RSV-seronegative infants and children) will remain on study until they complete the post-RSV season visit between April 1 and April 30 in the calendar year following enrollment. Participants in Group 2 will also attend several study visits during the time they are enrolled in the study. Study visits for all participants may include clinical assessments, blood collection, and nasal washes.