Evaluating the Infectivity, Safety and Immunogenicity of a Recombinant Live-Attenuated Respiratory Syncytial Virus Vaccine in RSV-Seronegative Infants 6 to 24 Months of Age

Inclusion Criteria

• Greater than or equal to 6 months (defined as greater than or equal to 180 days) of age at the time of screening and less than 25 months (defined as less than 750 days) of age.
• Good health based on review of the medical record, history, and physical examination, without evidence of chronic disease.
• Parents/guardians willing and able to provide written informed consent as described in the protocol.
• Seronegative for RSV antibody, defined as a serum RSV-neutralizing antibody titer less than 1:40 at screening from a sample collected no more than 42 days prior to inoculation.
• Growing at a normal velocity for age (as demonstrated on a standard growth chart) AND
• If less than 1 year of age: current height and weight above the 5th percentile
• If 1 year of age or older: current height and weight above the 3rd percentile for age.
• Received routine immunizations appropriate for age (as per national Center for Disease Control Advisory Committee on Immunization Practices [ACIP]).
• Expected to be available for the duration of the study.
• If born to an HIV-infected woman, participant must not have been breastfed and must have had documentation of 2 negative HIV nucleic acid (RNA or DNA) test results from samples collected on different dates with both collected when greater than or equal to 1 month of age and at least one collected when greater than or equal to 4 months of age, and no positive HIV nucleic acid (RNA or DNA) test; or 2 negative HIV antibody tests, both from samples collected at greater than or equal to 6 months of age.

Exclusion Criteria

• Known or suspected HIV infection or impairment of immunological functions.
• Receipt of immunosuppressive therapy, including any systemic, including either nasal or inhaled, corticosteroids within 28 days of enrollment. Note: Cutaneous (topical) steroid treatment was not an exclusion.
• Bone marrow/solid organ transplant recipient.
• Major congenital malformations (such as congenital cleft palate) or cytogenetic abnormalities.
• Previous receipt of a licensed or investigational RSV vaccine (or placebo in the IMPAACT 2011 study) or previous receipt of or planned administration of any anti-RSV product (such as ribavirin or RSV IG or RSV mAb).
• Previous anaphylactic reaction.
• Previous vaccine-associated adverse reaction that was Grade 3 or above.
• Known hypersensitivity to any study product component.
• Heart disease. Note: Participants with cardiac abnormalities documented to be clinically insignificant and requiring no treatment may be enrolled.
• Lung disease, including any history of reactive airway disease or medically documented wheezing.
• Member of a household that contained, or would contain, an infant who is less than 6 months of age at the enrollment date through Day 28.
• Member of a household that contains another child who is, or is scheduled to be, enrolled in IMPAACT 2011, 2012 or 2013 AND there had been or would be an overlap in residency during that other child's participation in the study's Acute Phase (Days 0 to 28).
• Member of a household that contains an immunocompromised individual, including, but not limited to:
• a person who was greater than or equal to 6 years of age with HIV-related immunodeficiency, defined as having a most recent CD4 T lymphocyte cell count less than 300 cells/mm^3. CD4 T lymphocyte count must have been measured within 6 months prior to enrollment, or
• a person age 1 year up to less than 6 years with HIV-related immunodeficiency, defined as having a most recent CD4 T lymphocyte cell percentage less than 25 or CD4 T lymphocyte count less than 750 cells/mm^3 (if both values are available, use the lower of the two). CD4 T lymphocyte parameter must have been measured within the 6 months prior to enrollment; or
• a person age less than 1 year with HIV-related immunodeficiency, defined as having a most recent CD4 T lymphocyte cell percentage less than 30 or CD4 T lymphocyte count less than 1000 cells/mm^3 (if