Evaluating the Infectivity, Safety, and Immunogenicity of the Recombinant Live-Attenuated Respiratory Syncytial Virus (RSV) Vaccines RSV ΔNS2/Δ1313/I1314L or RSV 276 in RSV-Seronegative Infants and Children 6 to 24 Months of Age

Human respiratory syncytial virus (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 infectivity, safety, and immunogenicity of two recombinant live-attenuated
RSV vaccines: RSV ΔNS2/Δ1313/I1314L and RSV 276. The vaccines will be delivered as nose drops
to RSV-seronegative infants and children 6 to 24 months of age.

Participants will be randomly assigned to receive a single dose of the RSV ΔNS2/Δ1313/I1314L
vaccine, the RSV 276 vaccine, or placebo at study entry (Day 0).

Participants will be enrolled in the study outside of RSV season, i.e., between April 1 and
October 31. All participants 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'
total study duration is between 6 and 13 months, depending on when they enroll in the study.

Participants will attend several study visits throughout the study, which may include
physical examinations, blood collection, nasal washes, and nasal adsorption (nasosorption)
specimen collection. Participants' parents or guardians will be contacted by study staff at
various times during the study to monitor participants' health.

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 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 as described
in the protocol.

- Seronegative for respiratory syncytial virus (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. Note: results from specimens collected during
screening for any study of an RSV vaccine developed by the Laboratory of Infectious
Diseases (LID) (NIAID, NIH) are acceptable as long as within the 42-day window.

- Growing normally for age (i.e., not downwardly crossing two major centiles on a
standard growth chart) in the six months prior to enrollment AND

- If less than 1 year of age: has a current height and weight above the 5th
percentile

- If 1 year of age or older: has a current height and weight above the 3rd
percentile for age.

- Has received routine immunizations appropriate for age (as per national Center for
Disease Control Advisory Committee on Immunization Practices [ACIP]). Note: if
rotavirus immunization was delayed, "catch-up" rotavirus immunization is indicated
only if the participant is age-eligible per ACIP.

- Is expected to be available for the duration of the study.

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 is not an exclusion.

- Any receipt of bone marrow/solid organ transplant.

- Major congenital malformations (such as congenital cleft palate) or cytogenetic
abnormalities.

- Previous receipt of a licensed or investigational RSV vaccine (or placebo in any
International Maternal Pediatric Adolescent AIDS Clinical Trials Network (IMPAACT) RSV
study) or previous receipt of or planned administration of any anti-RSV product (such
as ribavirin or RSV IG or RSV mAb).

- Any previous anaphylactic reaction.

- Any previous vaccine-associated adverse reaction that was Grade 3 or above. Note: if
grading is not possible, determine if the reaction was considered severe or life
threatening; if so, it is exclusionary.

- Any 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 diagnosed
wheezing.

- Member of a household that contains, or will 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/other children who is/are, or is/are
scheduled to be, enrolled in IMPAACT 2018 AND the date of enrollment to IMPAACT 2018
will not be concurrent with the other participant(s) living in the household (i.e.,
all eligible children from the same household must be enrolled on the same date).

- Member of a household that contains another child who is, or is scheduled to be,
enrolled in another study evaluating an intranasal live-attenuated RSV vaccine, AND
there has been or will 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 is HIV infected

- a person who has received chemotherapy within the 12 months prior to enrollment

- a person receiving immunosuppressant agents

- a person living with a solid organ or bone marrow transplant.

- Attends a daycare facility and shares a room with infants less than 6 months of age,
and parent/guardian is unable or unwilling to suspend daycare for 28 days following
inoculation.

- Any of the following events at the time of enrollment:

- fever (temporal or rectal temperature of greater than or equal to 100.4 degrees
F), or

- upper respiratory signs or symptoms (rhinorrhea, cough, or pharyngitis) or

- nasal congestion significant enough to interfere with successful inoculation, or

- otitis media.

- Receipt of the following prior to enrollment:

- any 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

- Scheduled administration 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 immunoglobulin, any antibody products, or any blood products within the
past 6 months prior to enrollment

- Receipt of any of the following medications within 3 days prior to study enrollment:

- systemic antibacterial, antiviral, antifungal, anti-parasitic, or antituberculous
agents, whether for treatment or prophylaxis, or

- intranasal medications, or

- other prescription medication except as 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.

- Receipt of salicylate (aspirin) or salicylate-containing products within the 28 days
prior to enrollment.

- Born at less than 34 weeks gestation.

- Born at less than 37 weeks gestation and less than 1 year of age at the time of
enrollment.

- Current suspected or documented developmental disorder, delay, or other developmental
problem.

- Any previous receipt of supplemental oxygen therapy in a home setting.