A Study to Determine the Safety and Efficacy of the RSV F Vaccine to Protect Infants Via Maternal Immunization

Inclusion Criteria

• ≥18 and ≤40 years-of-age
• Singleton pregnancy of 28 to 36 0/7 weeks gestation on the day of planned vaccination
• Documentation of gestational age will be based on one of the following composite criteria. (Note: The Investigator was to use the earliest ultrasound data available to establish the study-specific gestational age dating):
• Gestational Age Dating Based on First Trimester Data (data obtained ≤13 6/7 weeks): The date of the first day of the reported last menstrual period (LMP) may be used to establish the gestational age if corroborated by a first trimester ultrasound. If the gestational age estimation derived using the LMP and the first trimester ultrasound are discrepant >7 days, the ultrasound will be used to establish gestational age. If LMP is uncertain or unknown, the ultrasound-established gestational age estimation will be used to establish the gestational age of the pregnancy.
• Gestational Age Dating Based on Early Second Trimester Data (data obtained 14 0/7 to 21 6/7 weeks): The day of the first reported LMP may be used to establish the gestational age if corroborated by an early second trimester ultrasound (that estimates the gestational age between 14 0/7 and 21 6/7 weeks). If the gestational age estimation derived using the LMP and the early second trimester ultrasound are discrepant >10 days, the ultrasound will be used to establish the gestational age. If LMP is uncertain or unknown, the ultrasound-established gestational age estimation will be used to establish the gestational age of the pregnancy.
• Gestation Age Dating Based on Later Second Trimester Data (data obtained 22 0/7 and 27 6/7 weeks by LMP): The date of the first day of the reported LMP may be used to establish the gestation age if corroborated by a later second trimester ultrasound (that estimates the gestational age between 22 0/7 and 27 6/7 weeks). If the gestational age estimation derived using the LMP and the later second trimester ultrasound are discrepant >14 days, the ultrasound will be used to establish the gestational age. If LMP is uncertain or unknown, the ultrasound-established gestational age estimation will be used to establish the gestational age of the pregnancy.
• Gestational Age Dating When the LMP is Uncertain or Unknown AND No Prior First or Second Trimester Ultrasound Has Been Performed: An ultrasound performed at screening within the second trimester (≤27 6/7 weeks) will be used to establish the gestational age of the pregnancy.
• Documentation of a second or third (between 18 0/7 weeks and prior to randomization) trimester ultrasound with no major fetal anomalies identified.
• Good general maternal health as demonstrated by:
• Medical history (including history of adverse reactions to prior vaccines and allergies).
• Physical examination including at least vital signs (blood pressure, pulse, respirations, and oral temperature); weight; height; examination of the HEENT, cardiovascular, pulmonary, gastrointestinal (abdominal), musculoskeletal, lymphatic, and dermatologic organ systems; and documentation of fetal heart tones. Note that abnormal vital signs may be repeated at the investigator's discretion since these measures may be labile. Vital signs should be assessed in the context of normal values for the third trimester of pregnancy (see the Study Operations Manual).
• Clinical laboratory parameters that include:
• For the first year of study conduct in any country, normal/clinically insignificant blood urea nitrogen (BUN), creatinine, alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin, alkaline phosphatase (ALP), hemoglobin, white blood count, and platelet count. Note that normal ranges for clinical laboratory parameters will be based on reference ranges appropriate for the subject population under study (i.e., third trimester of pregnancy) and as defined in the toxicity grading scale (TGS) (see the Study Operations Manual).
• For all subjects,