Evaluating the Infectivity, Safety and Immunogenicity of a Recombinant Live-Attenuated Respiratory Syncytial Virus Vaccine, LID/ΔM2-2/1030s, in RSV-Seronegative Infants and Children 6 to 24 Months of Age

The purpose of this study is to evaluate the infectivity, safety, and immunogenicity of a single dose of a recombinant, live-attenuated respiratory syncytial virus (RSV) vaccine, LID/ΔM2-2/1030s, in RSV-seronegative infants and children 6 to 24 months of age.

This study will evaluate the infectivity, safety, and immunogenicity of a single dose of a recombinant, live-attenuated respiratory syncytial virus (RSV) vaccine, LID/ΔM2-2/1030s, in RSV-seronegative infants and children 6 to 24 months of age.

Participants will be randomly assigned to one of two groups to receive a single dose of intranasal RSV LID/ΔM2-2/1030s vaccine or placebo at study entry (Day 0). Group 1 (intensive) and Group 2 (less intensive) will differ only in the frequency of study visits and nasal swab collections.

Participants will receive study product between April 1 and October 15, outside of the RSV season, and will remain on the study until they complete the post-RSV season visit between April 1 and April 30 in the calendar year following enrollment. Participants' total study duration is between 6 and 13 months, depending upon time of enrollment.

Participants will attend several study visits throughout the study, which may include blood collection, nasal swabs, and physical examinations. Some of these visits may be remote if a stay at home order is put in place after enrollment.

Eligibility Criteria:
Inclusion Criteria:

* ≥ 6 months of age and \<25 months of age at the time of inoculation
* Screening and pre-inoculation serum specimens for respiratory syncytial virus (RSV)-neutralizing antibody are obtained no more than 42 days prior to inoculation
* Seronegative for RSV antibody, defined as serum RSV-neutralizing antibody titer \<1:40
* In good health based on review of the medical record, history, and physical examination at the time of inoculation
* Received routine immunizations appropriate for age based on the Advisory Committee on Immunization Practices (ACIP) Recommended Immunization Schedule for Children and Adolescents Aged 18 Years or Younger
* Growing normally for age as demonstrated on a World Health Organization (WHO) growth chart, AND

  * If \< 1 year of age: has a current height and weight above the 5th percentile for age
  * If ≥ 1 year of age: has a current height and weight above the 3rd percentile for age
* Expected to be available for the duration of the study
* Parent/guardian is willing and able to provide written informed consent

Exclusion Criteria:

* ≤ 6 months of age and \> 25 months of age at the time of inoculation
* Born at less than 34 weeks gestation
* Born at less than 37 weeks gestation, and at the date of inoculation less than 1 year of age
* Maternal history of a positive HIV test before or during pregnancy
* Evidence of chronic disease
* Known or suspected infection or impairment of immunological functions
* Bone marrow/solid organ transplant recipient
* Major congenital malformations, including congenital cleft palate or cytogenetic abnormalities
* Suspected or documented developmental disorder, delay, or other developmental problem
* Cardiac abnormality requiring treatment
* Lung disease or reactive airway disease
* More than one episode of medically diagnosed wheezing in the first year of life
* Wheezing episode or received bronchodilator therapy within the past 12 months
* Wheezing episode or received bronchodilator therapy after the age of 12 months
* Previous receipt of supplemental oxygen therapy in a home setting
* Previous receipt of an investigational RSV vaccine
* Previous receipt or planned administration of anti-RSV antibody product including ribavirin, RSV Ig, or RSV mAb
* Previous receipt of immunoglobulin or any antibody products within the past 6 months
* Previous receipt of any blood products within the past 6 months
* Previous anaphylactic reaction
* Previous vaccine-associated adverse reaction that was Grade 3 or above
* Known hypersensitivity to any study product component
* Member of a household that contains an infant who is less than 6 months of age at the date of inoculation through the 28th day after inoculation
* Member of a household that, at the date of inoculation through the 28th day after inoculation, contains an immunocompromised individual including but not limited to:

  * a person who is HIV-infected
  * a person who has cancer and has received chemotherapy within the 12 months prior to enrollment
  * a person living with a solid organ or bone marrow transplant
* Attends a daycare facility that does not separate children by age and contains an infant \<6 months of age at the date of inoculation through the 28th day after inoculation
* Receipt of any of the following prior to enrollment:

  * inactivated influenza vaccine within 3 days prior, or
  * any other inactivated vaccine or live-attenuated rotavirus vaccine within the 14 days prior, or
  * any live vaccine, other than rotavirus vaccine, within the 28 days prior, or
  * another investigational vaccine or investigational drug within 28 days prior, or
  * salicylate (aspirin) or salicylate-containing products within the past 28 days
* Scheduled administration of any of the following after planned inoculation

  * inactivated vaccine or live-attenuated rotavirus vaccine within the 14 days after, or
  * any live vaccine other than rotavirus in the 28 days after, or
  * another investigational vaccine or investigational drug in the 56 days after
* Receipt of any of the following medications within 3 days of study enrollment:

  * systemic antibacterial, antiviral, antifungal, anti-parasitic, or antituberculous agents, whether for treatment or prophylaxis, or
  * intranasal medications, or
  * other prescription medications except the permitted concomitant medications listed below
* Permitted concomitant medications (prescription or non-prescription) include nutritional supplements, medications for gastroesophageal reflux, eye drops, and topical medications, including (but not limited to) cutaneous (topical) steroids, topical antibiotics, and topical antifungal agents.
* Any of the following events at the time of enrollment:

  * fever (temporal or rectal temperature of ≥100.4°F), or
  * upper respiratory signs or symptoms (rhinorrhea, cough, or pharyngitis) or
  * nasal congestion significant enough to interfere with successful inoculation, or
  * otitis media
  * contact with a person diagnosed with COVID-19 disease or active severe acute respiratory syndrome coronavirus 2 (SARS CoV-2) infection within the preceding 10 days