A Clinical Trial on Safety in Pregnant Women and How Well the Infant is Protected Against RSV-associated Lower Respiratory Tract Infection When the Pregnant Woman Receives the Approved RSV Vaccine Compared to a Placebo.

Inclusion Criteria: * Pregnant women considered to be legally competent, as per country legislation, to consent for trial participation for herself and her newborn * Gestational age ≥ 28wk0days to \<36wks0days as per GAIA LOC criteria 1 to 2B who are not in active labour * Mother is able to understand and comply with planned trial procedures * Mother is attending ante-natal clinic * Mother has documented test for HIV and syphilis during the current pregnancy, * Provides written informed consent prior to initiation of trial. If the maternal participant is illiterate, a witnessed thumb-printed informed consent is acceptable * Intention to deliver at a hospital or birthing facility where trial procedures can be obtained (for immunogenicity cohort) * Expected to be available for the duration of the trial and can be contacted by telephone or by physical visit during trial participation * Participant is willing to give informed consent for her infant to participate in the trial Exclusion Criteria: * Body mass index of \>40 kg/m2 at the time of the first obstetric visit during the current pregnancy * Bleeding diathesis or condition (past or present) associated with prolonged bleeding that would, in the opinion of the investigator, contra-indicate intramuscular injection * History of severe adverse reaction associated with a vaccine * Current pregnancy complications or abnormalities at the time of consent that will increase the risk associated with the participation in and completion of the trial, including but not limited to the following: 1. More than two fetuses (i.e. twins will be allowed) 2. Preeclampsia, eclampsia, or uncontrolled gestational hypertension 3. Placental abnormality. 4. Polyhydramnios or oligohydramnios 5. Endocrine disorders, including untreated hyperthyroidism or untreated hypothyroidism, or uncontrolled diabetes mellitus at the time of consent. 6. Any signs of premature labour with the current pregnancy or having ongoing intervention (medical/ surgical) in the current pregnancy to prevent preterm birth. * At least THREE prior pregnancy complications or abnormalities at the time of consent, based on the investigator's judgment, that will increase the risk associated with the participation in and completion of the trial, including but not limited to the following: 1. Prior preterm delivery between 18 to ≤34 weeks gestation, or birth weight \<2200 grams. 2. Prior stillbirth or neonatal death within 7 days of birth. 3. Previous infant with a known genetic disorder or major congenital anomaly * Mother who is positive for syphilis and untreated at time of enrolment * Mother living with HIV/AIDS considered to have WHO Clinical Stage 3 or 4 AIDS, or considered to be clinically unstable * Major illness of the maternal participant or conditions of the foetus that, in the investigator's judgment, will substantially increase the risk associated with the maternal participant's participation in, and completion of, the trial * Congenital or acquired immunodeficiency disorder, or rheumatologic disorder or other illness requiring chronic treatment with known immunosuppressant medications, including monoclonal antibodies, within the year prior to enrolment * Other acute or chronic medical or psychiatric condition including recent (within the past year) or active suicidal ideation or behaviour or laboratory abnormality that may increase the risk associated with trial participation and, in the judgment of the investigator, would make the participant inappropriate for entry into this trial * Participation in other studies involving investigational drug(s) within 28 days prior to consent and/or during trial participation. * Use of systemic corticosteroids for \>14 days within 28 days prior to trial enrolment. Prednisone use of \<20 mg/day for ≤14 days is permitted. Inhaled/nebulized, intra-articular, intra-bursal, or topical (skin or eyes) corticosteroids are permitted * Current alcohol abuse or illicit drug use * Receipt of blood or plasma products or immunoglobulin (Ig) in past 60 days or planned receipt through delivery, with exception of Rho(D) immune globulin (eg, RhoGAM), which can be given at any time * Previous vaccination with any licensed or investigational RSV vaccine or planned receipt during trial participation