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.

Analysis was performed on the Solicited Safety Set, which included all maternal participants who received 1 dose of a study intervention and who had solicited safety data available during the specified period.

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.

Analysis was performed on the Solicited Safety Set, which included all maternal participants who received 1 dose of a study intervention and who had solicited safety data available during the specified period.

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.

Analysis was performed on the Exposed Set - Maternal, which included all maternal participants who received 1 dose of a study intervention.

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.

Analysis was performed on the Exposed Set - Maternal, which included all maternal participants who received 1 dose of a study intervention.

A participant was considered to have withdrawn from the study if no new study procedure had been performed or no new information had been collected for her since the date of withdrawal/last contact.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.

Analysis was performed on the Exposed Set - Maternal, which included all maternal participants who received 1 dose of a study intervention.

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.

Analysis was performed on the Exposed Set - Maternal, which included all maternal participants who received 1 dose of a study intervention.

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.

Analysis was performed on the Exposed Set - Infant, which included infants live-born to exposed maternal participants, whose parents/legally acceptable representatives (LARs) completed the informed consent process and signed the informed consent form.

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.

Analysis was performed on the Exposed Set - Maternal, which included all maternal participants who received 1 dose of a study intervention.

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.

Analysis was performed on the Exposed Set - Maternal, which included all maternal participants who received 1 dose of a study intervention.

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).

Analysis was performed on the Exposed Set - Infant, which included infants live-born to exposed maternal participants, whose parents/LARs completed the informed consent process and signed the informed consent form.

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.

Analysis was performed on the Exposed Set - Infant, which included infants live-born to exposed maternal participants, whose parents/LARs completed the informed consent process and signed the informed consent form.

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.

Analysis was performed on the Exposed Set - Infant, which included infants live-born to exposed maternal participants, whose parents/LARs completed the informed consent process and signed the informed consent form.

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.

Analysis was performed on the Exposed Set - Infant, which included infants live-born to exposed maternal participants, whose parents/LARs completed the informed consent process and signed the informed consent form.

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.

Analysis was performed on the Exposed Set - Infant, which included infants live-born to exposed maternal participants, whose parents/LARs completed the informed consent process and signed the informed consent form.

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.

Analysis was performed on the Exposed Set - Infant, which included infants live-born to exposed maternal participants, whose parents/LARs completed the informed consent process and signed the informed consent form.

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.

Analysis was performed on the Exposed Set - Infant, which included infants live-born to exposed maternal participants, whose parents/LARs completed the informed consent process and signed the informed consent form.

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.

Analysis was performed on the Exposed Set - Infant, which included infants live-born to exposed maternal participants, whose parents/LARs completed the informed consent process and signed the informed consent form.

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.

Analysis was performed on the Exposed Set - Infant, which included infants live-born to exposed maternal participants, whose parents/LARs completed the informed consent process and signed the informed consent form.

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.

Analysis was performed on the Exposed Set - Infant, which included infants live-born to exposed maternal participants, whose parents/LARs completed the informed consent process and signed the informed consent form.

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).

Analysis was performed on the Per Protocol Set Immunogenicity - Maternal, which included all maternal participants who received 1 dose of a study intervention and had immunogenicity data available for the specified analysis at the specified time point (i.e. pre-dosing [Day 1]), minus those participants with protocol deviations that lead to exclusion.

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

Analysis was performed on the Per Protocol Set Immunogenicity - Maternal, which included all maternal participants who received 1 dose of a study intervention and had immunogenicity data available for the specified analysis at the specified time point (i.e. delivery), minus those participants with protocol deviations that lead to exclusion.

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

Analysis was performed on the Per Protocol Set Immunogenicity - Maternal, which included all maternal participants who received 1 dose of a study intervention and had immunogenicity data available for the specified analysis at the specified time point (i.e. pre-dosing [Day 1]), minus those participants with protocol deviations that lead to exclusion.

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

Analysis was performed on the Per Protocol Set Immunogenicity - Maternal, which included all maternal participants who received 1 dose of a study intervention and had immunogenicity data available for the specified analysis at the specified time point (i.e. delivery), minus those participants with protocol deviations that lead to exclusion.

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).

Analysis was performed on all pairs of maternal participants (from Per Protocol Set Immunogenicity - Maternal) and their infants (from Per Protocol Set Immunogenicity - Infant) with available results for this outcome measure at the specified time points.

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).

Analysis was performed on the Per Protocol Set Immunogenicity - Infant, which included all infant participants in the Exposed set who had post-delivery/birth immunogenicity data available for the specified analysis at the specified time points, minus those who (a) were born less than 4 weeks post-maternal participant dosing and/ or (b) had protocol deviations that lead to exclusion.

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).

Analysis was performed on the Per Protocol Set Immunogenicity - Infant, which included all infant participants in the Exposed set who had post-delivery/birth immunogenicity data available for the specified analysis at the specified time points, minus those who (a) were born less than 4 weeks post-maternal participant dosing and/ or (b) have protocol deviations that lead to exclusion.

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.

Analysis was performed on the Exposed Set - Maternal, which included all maternal participants who received 1 dose of a study intervention.

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.

Analysis was performed on the Exposed Set - Maternal, which included all maternal participants who received 1 dose of a study intervention.

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.

Analysis was performed on the Exposed Set - Maternal, which included all maternal participants who received 1 dose of a study intervention.

Worsening of pre-existing medical condition and/or obstetric complication was considered by the investigator, using clinical judgement 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.

Analysis was performed on the Exposed Set - Maternal, which included all maternal participants who received 1 dose of a study intervention.

RSV-associated MA-RTI was defined as a medically attended visit for RTI symptoms and confirmed RSV infection.

Analysis was performed on the Exposed Set - Maternal, which included all maternal participants who received 1 dose of a study intervention.

An RSV-associated LRTI is characterized by a history of cough OR difficulty in breathing, AND a blood oxygen saturation by pulse oximetry (SpO2) lower than (<) 95%, OR respiratory rate increase AND a confirmed RSV infection. An RSV-associated severe LRTI meets the case definition of RSV-LRTI AND is additionally characterized by a SpO2 <93%, OR lower chest wall in-drawing, OR inability to feed, OR failure to respond/unconscious.

Analysis was performed on the Exposed Set - Infant, which included infants live-born to exposed maternal participants, whose parents/LARs completed the informed consent process and signed the informed consent form.

RSV-associated hospitalization was defined as a confirmed RSV infection and hospitalized for acute medical condition. Hospitalization was defined as admission for observation or treatment based on the judgment of a health care provider.

Analysis was performed on the Exposed Set - Infant, which included infants live-born to exposed maternal participants, whose parents/LARs completed the informed consent process and signed the informed consent.

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

Analysis was performed on the Per Protocol Set Immunogenicity - Maternal, which included all maternal participants who received 1 dose of a study intervention and had immunogenicity data available for the specified analysis at the specified time point (i.e. Day 31 post-dosing), minus those participants with protocol deviations that lead to exclusion.

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

Analysis was performed on the Per Protocol Set Immunogenicity - Maternal, which included all maternal participants who received 1 dose of a study intervention and had immunogenicity data available for the specified analysis at the specified time point (i.e. Day 31 post-dosing), minus those participants with protocol deviations that lead to exclusion.

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

Analysis was performed on the Per Protocol Set Immunogenicity - Maternal, which included all maternal participants who received 1 dose of a study intervention and had immunogenicity data available for the specified analysis at the specified time points, minus those participants with protocol deviations that lead to exclusion.

RSV-B 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).

Analysis was performed on the Per Protocol Set Immunogenicity - Infant, which included all infant participants in the Exposed set who had post-delivery/birth immunogenicity data available for the specified analysis at the specified time points, minus those who (a) were born less than 4 weeks post-maternal participant dosing and/ or (b) had protocol deviations that lead to exclusion.

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

Analysis was performed on a sub-cohort from the Per Protocol Set Immunogenicity - Infant, which included the infant participants for whom blood samples were collected for the specified analysis at Day 43 post-birth.

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

Analysis was performed on a sub-cohort from the Per Protocol Set Immunogenicity - Infant, which included the infant participants for whom blood samples were collected for the specified analysis at Day 121 post-birth.

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

Analysis was performed on a sub-cohort from the Per Protocol Set Immunogenicity - Infant, which included the infant participants for whom blood samples were collected for the specified analysis at Day 181 post-birth. There was only one participant in the Control Group - Infant for whom blood sample was collected, hence the 95% confidence interval (CI) associated with geometric mean could not be calculated for single participant.

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

Analysis was performed on a sub-cohort from the Per Protocol Set Immunogenicity - Infant, which included the infant participants for whom blood samples were collected for the specified analysis at Day 43 post-birth.

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

Analysis was performed on a sub-cohort from the Per Protocol Set Immunogenicity - Infant, which included the infant participants for whom blood samples were collected for the specified analysis at Day 121 post-birth.

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

Analysis was performed on a sub-cohort from the Per Protocol Set Immunogenicity - Infant, which included the infant participants for whom blood samples were collected for the specified analysis at Day 181 post-birth. There was only one participant in the Control Group - Infant for whom blood sample was collected, hence the 95% confidence interval (CI) associated with geometric mean could not be calculated for single participant.

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

Analysis was performed on a sub-cohort from the Per Protocol Set Immunogenicity - Infant, which included the infant participants for whom blood samples were collected for the specified analysis at Day 43 post-birth.

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

Analysis was performed on a sub-cohort from the Per Protocol Set Immunogenicity - Infant, which included the infant participants for whom blood samples were collected for the specified analysis at Day 121 post-birth.

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

Analysis was performed on a sub-cohort from the Per Protocol Set Immunogenicity - Infant, which included the infant participants for whom blood samples were collected for the specified analysis at Day 181 post-birth. There was only one participant in the Control Group - Infant for whom blood sample was collected, hence the 95% confidence interval (CI) associated with geometric mean could not be calculated for single participant.