Research Studies

The study will be conducted in children at selected sites in the United States. The vaccines will be evaluated in RSV-seronegative children ≥6 months (180 days) at the time of screening to <25 months (750 days) of age at the time of enrollment. Hypothesis: The live-attenuated RSV vaccine candidates RSV ΔNS2/Δ1313/I1314L, RSV 6120/ΔNS2/1030s, and RSV 276 will each be safe and immunogenic in RSV-seronegative recipients. However, these vaccine candidates may have safety signals that become apparent only when analyzed in a larger number of participants, and the candidates may differ in the magnitude and longevity of antibody responses, and in responses observed following naturally occurring RSV infection. To move forward, the vaccines should: be safe, and result in at least 70% of the population of vaccine recipients having a ≥4-fold rise in serum RSV-neutralizing antibody titers from pre-study product administration to the Day 56 Visit after study product administration The primary objectives of this study are the following: To estimate and compare (each vaccine group to placebo) the frequency and severity of adverse events (AEs) following study product administration (Day 0) through Day 56 To estimate and compare (between the vaccine groups and to the benchmark of 70%) the percentage of vaccinees having a ≥4-fold rise in serum RSV-neutralizing antibodies at the Day 56 Visit The secondary objectives of this study are to: To estimate and compare (between the vaccine groups) the percentage of vaccinees with a ≥4-fold rise in serum IgG antibody to RSV F protein (RSV F IgG) at the Day 56 Visit To estimate and compare (between the vaccine groups) the titers of serum RSV F IgG and serum RSV-neutralizing antibodies at the Day 56 Visit To describe and compare the frequency and severity of RSV-associated, medically attended, acute respiratory illness (RSV-MAARI) and RSV-associated, medically attended, acute lower respiratory illness (RSV-MAALRI) in the placebo and vaccine arms during RSV season. Potential participants must meet all of the following criteria in order to be included in this study: ≥6 months (defined as ≥180 days) of age at the time of screening and <25 months (defined as < 750 days) of age at the time of enrollment. In good health based on review of the medical record, history, and physical examination, without evidence of chronic disease. Parent/guardian is willing and able to provide written informed consent Seronegative for RSV antibody, defined as a serum RSV-neutralizing antibody titer <1:40 at screening from a sample collected no more than 42 days prior to study product administration. Growing normally for age in the opinion of the site clinician in the six months prior to enrollment AND has a current height and weight above the 3rd percentile for age and sex per CDC (WHO) growth standards. Has received routine immunizations appropriate for age (as per national Center for Disease Control Advisory Committee on Immunization Practices [ACIP]). Note: COVID-19 vaccination will not be required unless fully licensed for this age group and ACIP-recommended. See MOP for further guidance. Is expected to be available for the duration of the study. If born to an HIV-infected woman, potential participant must have documentation of 2 negative HIV nucleic acid (RNA or DNA) test results from samples collected on different dates with both collected when ≥4 weeks of age and at least one collected when ≥16 weeks of age, and no positive HIV nucleic acid (RNA or DNA) test; or 2 negative HIV antibody tests, both from samples collected at ≥24 weeks of age. If potential participant was breastfed by an HIV-infected woman, each of the sampling times noted above must be measured in weeks after the last exposure to breast milk, rather than weeks of age.