Results are presented as confirmed by endpoint adjudication committee. Severe MA-LRTI cases were a subset of MA-LRTI cases, and all severe MA-LRTI cases included MA-LRTI cases. Severe MA-LRTI case was an RSV positively adjudicated event which met the following defined criteria: an infant with an MA-RTI visit and aged associated fast breathing (RR >=70 bpm for <2 months of age [<60 days of age], >=60 bpm for >=2 months to <12 months of age, or >=50 bpm for >=12 months to 24 months of age) or SpO2 <93% or high-flow nasal cannula or mechanical ventilation (i.e., invasive or non-invasive) or intensive care unit (ICU) admission for more than (>) 4 hours or failure to respond/unconscious.

Results are presented as confirmed by endpoint adjudication committee. Severe MA-LRTI cases were a subset of MA-LRTI cases, and all severe MA-LRTI cases were included MA-LRTI cases. Severe MA-LRTI case was an RSV positively adjudicated event which met the following defined criteria: an infant with an MA-RTI visit and aged associated fast breathing (RR >=70 bpm for <2 months of age [<60 days of age], >=60 bpm for >=2 months to <12 months of age, or >=50 bpm for >=12 months to 24 months of age) or SpO2 <93% or high-flow nasal cannula or mechanical ventilation (i.e., invasive or non-invasive) or ICU admission for >4 hours or failure to respond/unconscious.

Results are presented as confirmed by endpoint adjudication committee. Severe MA-LRTI cases were a subset of MA-LRTI cases, and all severe MA-LRTI cases were included MA-LRTI cases. Severe MA-LRTI case was an RSV positively adjudicated event which met the following defined criteria: an infant with an MA-RTI visit and aged associated fast breathing (RR >=70 bpm for <2 months of age [<60 days of age], >=60 bpm for >=2 months to <12 months of age, or >=50 bpm for >=12 months to 24 months of age) or SpO2 <93% or high-flow nasal cannula or mechanical ventilation (i.e., invasive or non-invasive) or ICU admission for >4 hours or failure to respond/unconscious.

Results are presented as confirmed by endpoint adjudication committee. Severe MA-LRTI cases were a subset of MA-LRTI cases, and all severe MA-LRTI cases were included MA-LRTI cases. Severe MA-LRTI case was an RSV positively adjudicated event which met the following defined criteria: an infant with an MA-RTI visit and aged associated fast breathing (RR >=70 bpm for <2 months of age [<60 days of age], >=60 bpm for >=2 months to <12 months of age, or >=50 bpm for >=12 months to 24 months of age) or SpO2 <93% or high-flow nasal cannula or mechanical ventilation (i.e., invasive or non-invasive) or ICU admission for >4 hours or failure to respond/unconscious.

AESI are a subset of targeted medical events based on review of known pharmacology, toxicology findings, possible class effects, published literature, and signals arising from safety data assessments, and on population under study. AESIs were based on targeted medical events associated with pregnant maternal participants and their infants prior to/during delivery and at birth. For infant participants the following were considered as protocol defined AESIs: Preterm birth (born at <37 weeks gestation); birth weight 1001-2500 grams; developmental delay; positive viral (polymerase chain reaction [PCR] or antigen-based) testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), when not reported during MA-RTI visit, were reported as SARS-CoV-2 test positive. Extremely preterm birth (<28 weeks) and extremely low birth weight (=<1000 grams [g]) were reported as serious AESIs.

Neonatal death was defined as the death of a live-born infant that occurred within a month after birth.

Congenital malformations/ anomalies were defined as structural or functional anomalies that occurred during intrauterine life and could be identified prenatally, at birth or later in life.

Other Neonatal problem included dysmaturity, neonatal illness, hospitalization, drug therapies, and neonatal death.

APGAR was a fast evaluation technique used to evaluate a newborn baby's overall health. APGAR stands for (A) Appearance (skin coloration), (P) Pulse (heart rate), (G) Grimace (reflex response), (A) Activity (muscle tone) and (R) Respiration (breathing). Each component was given a score of 0, 1, or 2; after summing up scores for each component a total possible score was of 0 (worst condition) to 10 (best condition), where higher scores indicate better health. A score of 7 to 10 was good, 4 to <7 was moderate, and <4 was poor.

APGAR was a fast evaluation technique used to evaluate a newborn baby's overall health. APGAR stands for (A) Appearance (skin coloration), (P) Pulse (heart rate), (G) Grimace (reflex response), (A) Activity (muscle tone) and (R) Respiration (breathing). Each component was given a score of 0, 1, or 2; after summing up scores for each component a total possible score was of 0 (worst condition) to 10 (best condition), where higher scores indicate better health. A score of 7 to 10 was good, 4 to <7 was moderate, and <4 was poor.

APGAR was a fast evaluation technique used to evaluate a newborn baby's overall health. APGAR stands for (A) Appearance (skin coloration), (P) Pulse (heart rate), (G) Grimace (reflex response), (A) Activity (muscle tone) and (R) Respiration (breathing). Each component was given a score of 0, 1, or 2; after summing up scores for each component a total possible score was of 0 (worst condition) to 10 (best condition), where higher scores indicate better health. A score of 7 to 10 was good, 4 to <7 was moderate, and <4 was poor.

An AE was any untoward medical occurrence in a participant or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention.

An AE was any untoward medical occurrence in a participant or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. An SAE was any untoward medical occurrence that at any dose: resulted in death, was life threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability/incapacity, resulted in congenital anomaly/birth defect or that was considered an important medical event. An NDCMC was defined as a disease or medical condition, not previously identified, that was expected to be persistent or otherwise long-lasting in its effects.

An AE was any untoward medical occurrence in a participant or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. An SAE was any untoward medical occurrence that at any dose: resulted in death, was life threatening required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability/incapacity, resulted in congenital anomaly/birth defect or that was considered an important medical event. An NDCMC was defined as a disease or medical condition, not previously identified, that was expected to be persistent or otherwise long-lasting in its effects.

An AE was any untoward medical occurrence in a participant or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. An SAE was any untoward medical occurrence that at any dose: resulted in death, was life threatening required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability/incapacity, resulted in congenital anomaly/birth defect or that was considered an important medical event. An NDCMC was defined as a disease or medical condition, not previously identified, that was expected to be persistent or otherwise long-lasting in its effects.

Local reactions included redness, swelling, and pain at injection site and were recorded in electronic diary (e-diary). Redness and swelling were measured and recorded in measuring device units. 1 measuring device unit= 0.5 centimetre (cm). Redness and swelling were graded as mild (>2.0 to 5.0 cm), moderate (>5.0 to 10.0 cm), severe (>10.0 cm) and grade 4 (necrosis or exfoliative dermatitis for redness and necrosis for swelling). Pain at injection site was graded as mild (did not interfere with activity), moderate (interfered with activity), severe (prevented daily activity) and grade 4 (emergency room visit or hospitalization for the severe pain at the injection site). Grade 4 reactions were classified by the investigator or medically qualified person.

Systemic events included: fever, fatigue, headache, nausea, muscle pain, joint pain, vomiting and diarrhea and were recorded by participants in an e-diary. Fever was defined as an oral temperature >=38.0 degree Celsius [C]) and classified as mild (38.0 to 38.4), moderate (38.5 to 38.9), severe (39.0 to 40.0) and grade 4 (>40.0 degree C). Headache, nausea, fatigue, muscle pain and joint pain were graded as mild (did not interfere with activity), moderate (some interference with activity), severe (prevented daily activity). Vomiting: mild (1-2 times in 24 hours [H]), moderate (>2 times in 24 H), severe (required intravenous [IV] hydration). Diarrhea: mild (2-3 loose stools in 24 H), moderate (4-5 loose stools in 24 H), severe (>=6 in 24 H). For all systemic events except fever, Grade 4= emergency room visit or hospitalization. Grade 4 events were classified by investigator or medically qualified person.

An AE was any untoward medical occurrence in a participant or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention Only AEs collected by non-systematic assessment (i.e. excluding local reactions and systemic events) were included in this outcome measure.

An AE was any untoward medical occurrence in a participant or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. An SAE was any untoward medical occurrence that at any dose: resulted in death, was life threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability/incapacity, resulted in congenital anomaly/birth defect or that was considered an important medical event.

Results are presented as confirmed by endpoint adjudication committee. MA-LRTI case: Infant with an MA-RTI visit with age related fast breathing (RR >=60 bpm for <2 months of age [<60 days of age], >=50 bpm for >=2 months to <12 months of age, or >=40 bpm for >=12 months to 24 months of age) or SpO2 <95% or chest wall indrawing and RSV positive test results by RT-PCR testing of midturbinate nasal swab samples.

Infant participants born to maternal participants vaccinated with a single dose of 120 mcg RSVpreF were included. Infant participants were all followed up for 12 months after birth, and for infants born to maternal participants during the first year of the study, they were followed up for 24 months after birth.

Infant participants born to maternal participants who received placebo (matching RSVpreF without active vaccine) were included. Infant participants were all followed up for 12 months after birth, and for infants born to maternal participants during the first year of the study, they were followed up for 24 months after birth.

Maternal safety population included all randomized maternal participants who received investigational product. Infant safety population included all infant participants who were born to vaccinated maternal participants.