A Phase III, Double-blind, Randomized, Placebo-controlled Study to Evaluate the Safety, Reactogenicity and Immune Response of a Single Intramuscular Dose of Unadjuvanted RSV Maternal Vaccine, in High Risk Pregnant Women Aged 15 to 49 Years and Infants Born to the Vaccinated Mothers

Percentage of Infant Participants Reporting MAEs From Birth up to 180 Days Post-birth

Time Frame: From birth up to 180 days post-birth

An MAE was defined as an unsolicited AE for which the participants received medical attention such as hospitalization, or an emergency room visit, or visit to/by a health care provider.

Percentage of Infant Participants Reporting Any SAEs From Birth up to 365 Days Post-birth

Time Frame: From birth up to 365 days post-birth

An SAE was defined as any untoward medical occurrence that resulted in death, was life-threatening, required hospitalization or prolongation of existing hospitalization, resulted in disability/incapacity, was a congenital anomaly/birth defect or resulted in other situations that were considered serious per medical or scientific judgment. Any = occurrence of any SAE regardless of intensity grade or relation to vaccination.

Percentage of Infant Participants Reporting MAEs From Birth up to 365 Days Post-birth

Time Frame: From birth up to 365 days post-birth

An MAE was defined as an unsolicited AE for which the participants received medical attention such as hospitalization, or an emergency room visit, or visit to/by a health care provider.

RSV MAT Immunoglobulin G (IgG)-Specific Antibody Concentrations for Maternal Participants at Pre-dosing (Day 1)

Time Frame: At pre-dosing (Day 1)

RSV MAT IgG-specific antibody concentrations were determined by enzyme-linked immunosorbent assay (ELISA) and expressed as geometric mean concentrations (GMCs) in ELISA units per milliliter (ELU/mL).

RSV-A Neutralizing Titers for Maternal Participants at Pre-dosing (Day 1)

Time Frame: At pre-dosing (Day 1)

RSV-A neutralizing titers were determined by neutralization assay and expressed as geometric mean titers (GMTs).

Percentage of Maternal Participants Reporting Any Solicited Systemic Events

Time Frame: From Day 1 to Day 7 included

Assessed solicited systemic events included abdominal pain, diarrhea, fatigue, headache, nausea, fever \[temperature equal to or above (\>=) 38 degrees Celsius (°C)/100.4 degrees Fahrenheit (°F), regardless of the location of measurement\] and vomiting. Any = occurrence of the adverse event regardless of intensity grade or relation to study vaccination.

Percentage of Maternal Participants Reporting Any Unsolicited Adverse Events (AEs)

Time Frame: From Day 1 to Day 30 included

An unsolicited AE was defined as any AE reported in addition to those solicited during the clinical study. Also, any 'solicited' symptom with onset outside the specified period of follow-up for solicited symptoms was reported as an unsolicited AE. Any = occurrence of any unsolicited AE regardless of intensity grade or relation to vaccination.

Percentage of Maternal Participants Reporting Any Serious Adverse Events (SAEs) From Day 1 up to 42 Days Post-delivery

Time Frame: From Day 1 up to 42 days post-delivery, an average of 2 months

An SAE was defined as any untoward medical occurrence that resulted in death, was life-threatening, required hospitalization or prolongation of existing hospitalization, resulted in disability/incapacity, was a congenital anomaly/birth defect in the offspring of a study participant or resulted in abnormal pregnancy outcomes or in other situations that were considered serious per medical or scientific judgment. Any = occurrence of any SAE regardless of intensity grade or relation to vaccination.

Number of Maternal Participants Reporting (S)AEs Leading to Study Withdrawal From Day 1 up to 42 Days Post-delivery

Time Frame: From Day 1 up to 42 days post-delivery, an average of 2 months

A participant was considered to have withdrawn from the study if no new study procedure had been performed or no new information had been collected for her since the date of withdrawal/last contact. (S)AEs leading to study withdrawal were (S)AEs identified by the investigator to cause participant withdrawal until the resolution of the event. These participant withdrawals were considered different from participant withdrawals for other reasons.

Percentage of Maternal Participants Reporting Medically Attended Adverse Events (MAEs) From Day 1 up to 42 Days Post-delivery

Time Frame: From Day 1 up to 42 days post-delivery, an average of 2 months

An MAE was defined as an unsolicited AE for which the participant received medical attention such as hospitalization, or an emergency room visit, or visit to/by a health care provider.

Percentage of Live Births With no Congenital Anomalies, Live Births With Minor Congenital Anomaly(Ies) and Live Births With at Least 1 Major Congenital Anomaly

Time Frame: From Day 1 up to 42 days post-delivery, an average of 2 months

The percentage of live births with no congenital anomalies, live births with minor congenital anomaly(ies) only and live births with at least 1 major congenital anomaly is reported.

Percentage of Maternal Participants Reporting Any Solicited Administration Site Events

Time Frame: From Day 1 to Day 7 included

Assessed solicited administration site events included erythema, pain and swelling. Any pain = occurrence of the symptom regardless of intensity grade. Any erythema and swelling = symptom reported with a surface diameter greater than or equal to 20 millimeters.

Percentage of Maternal Participants Reporting Pregnancy-related Adverse Events of Special Interest (AESIs) From Day 1 up to 42 Days Post-delivery

Time Frame: From Day 1 up to 42 days post-delivery, an average of 2 months

Pregnancy-related AESIs included preterm labor, provider-initiated preterm birth, premature preterm rupture of membranes, pre-eclampsia, pre-eclampsia with severe features including eclampsia, gestational hypertension and fetal growth restriction.

Percentage of Maternal Participants Reporting Worsening of Pre-existing Medical Conditions and/or Obstetric Complications From Day 1 up to 42 Days Post-delivery

Time Frame: From Day 1 up to 42 days post-delivery, an average of 2 months

Worsening of pre-existing medical condition and/or obstetric complication was considered by the investigator, using clinical judgment and the following criteria: * Change in medication and/or medication dose. * Medically attended event in relation to pre-existing condition and/or obstetric complication that are outside the routine management of the condition/complication. * SAE and/or hospitalization in relation to pre-existing condition and/or obstetric complication.

Percentage of Infant Participants Reporting Neonatal/Infant AESIs From Birth up to 42 Days Post-birth

Time Frame: From birth up to 42 days post-birth, an average of 2 months

Neonatal/infant AESIs included low birth weight (below \[\<\] 2500 grams), very low birth weight (\<1500 grams), extremely low birth weight (\<1000 grams), preterm birth (\<37 weeks of gestational age), small for gestational age (weight below 10th percentile for gestational age), congenital anomalies with internal structural defects and neonatal death in a preterm live birth (gestational age equal to or above \[\>=\] 28 and \<37 weeks).

Percentage of Infant Participants Reporting Any SAEs From Birth up to 42 Days Post-birth

Time Frame: From birth up to 42 days post-birth, an average of 2 months

An SAE was defined as any untoward medical occurrence that resulted in death, was life-threatening, required hospitalization or prolongation of existing hospitalization, resulted in disability/incapacity, was a congenital anomaly/birth defect or resulted in other situations that were considered serious per medical or scientific judgment. Any = occurrence of any SAE regardless of intensity grade or relation to vaccination.

Number of Infant Participants Reporting (S)AEs Leading to Study Withdrawal From Birth up to 42 Days Post-birth

Time Frame: From birth up to 42 days post-birth, an average of 2 months

A participant was considered to have withdrawn from the study if no new study procedure had been performed or no new information had been collected for her since the date of withdrawal/last contact. (S)AEs leading to study withdrawal were (S)AEs identified by the investigator to cause participant withdrawal until the resolution of the event. These participant withdrawals were considered different from participant withdrawals for other reasons.

Percentage of Infant Participants Reporting MAEs From Birth up to 42 Days Post-birth

Time Frame: From birth up to 42 days post-birth, an average of 2 months

An MAE was defined as an unsolicited AE for which the participants received medical attention such as hospitalization, or an emergency room visit, or visit to/by a health care provider.

Percentage of Infant Participants Reporting Any SAEs From Birth up to 180 Days Post-birth

Time Frame: From birth up to 180 days post-birth

An SAE was defined as any untoward medical occurrence that resulted in death, was life-threatening, required hospitalization or prolongation of existing hospitalization, resulted in disability/incapacity, was a congenital anomaly/birth defect or resulted in other situations that were considered serious per medical or scientific judgment. Any = occurrence of any SAE regardless of intensity grade or relation to vaccination.

RSV MAT IgG-specific Antibody Concentrations for Maternal Participants at Delivery

Time Frame: At delivery

RSV MAT IgG-specific antibody concentrations were determined by ELISA and expressed as GMCs in ELU/mL.

Number of Infant Participants Reporting (S)AEs Leading to Study Withdrawal From Birth up to 180 Days Post-birth

Time Frame: From birth up to 180 days post-birth

A participant was considered to have withdrawn from the study if no new study procedure had been performed or no new information had been collected for her since the date of withdrawal/last contact. (S)AEs leading to study withdrawal were (S)AEs identified by the investigator to cause participant withdrawal until the resolution of the event. These participant withdrawals were considered different from participant withdrawals for other reasons.

Number of Infant Participants Reporting (S)AEs Leading to Study Withdrawal From Birth up to 365 Days Post-birth

Time Frame: From birth up to 365 days post-birth

A participant was considered to have withdrawn from the study if no new study procedure had been performed or no new information had been collected for her since the date of withdrawal/last contact. (S)AEs leading to study withdrawal were (S)AEs identified by the investigator to cause participant withdrawal until the resolution of the event. These participant withdrawals were considered different from participant withdrawals for other reasons.

RSV-A Neutralizing Titers for Infant Participants at Delivery or Within 72 Hours After Birth

Time Frame: At delivery or within 72 hours after birth

RSV-A neutralizing titers were determined by neutralization assay and expressed as GMTs. The titers were measured on the cord blood sample collected at delivery, or on a blood sample collected from the infant within 72 hours after birth (if no cord blood sample could be obtained).

RSV-A Neutralizing Titers for Maternal Participants at Delivery

Time Frame: At delivery

RSV-A neutralizing titers were determined by neutralization assay and expressed as GMTs.

Geometric Mean Ratio (GMR) Between Cord Blood and Maternal RSV MAT IgG-specific Antibody Concentrations

Time Frame: At delivery (for maternal participants) or within 72 hours after birth (for infant participants)

The placental transfer ratio of IgG-specific antibody concentration was determined from cord blood (or infant blood sample collected within 72 hours after birth \[if no cord blood could be obtained\]) over that of the blood sample from mother at delivery (if no blood sample was collected during delivery).

RSV MAT IgG-specific Antibody Concentrations for Infant Participants at Delivery or Within 72 Hours After Birth

Time Frame: At delivery or within 72 hours after birth

RSV MAT IgG-specific antibody concentrations were determined by ELISA and expressed as GMCs in ELU/mL. The antibody concentrations were measured on the cord blood sample collected at delivery, or on a blood sample collected from the infant within 72 hours after birth (if no cord blood sample could be obtained).