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.
The purpose of this study is to evaluate the safety and immunogenicity of the RSV D46cpΔM2-2 vaccine in RSV-seropositive children and RSV-seronegative infants and children.