A Phase 3 Study of Revaccination in Subsequent Pregnancies With Bivalent RSV Vaccine and Duration of Protection of a Single Dose

Pregnant Participants-Cohort 1 and Cohort 2 Key Inclusion Criteria * Women aged 18 to 49 who are pregnant, between 24 and 36 weeks along, and expecting one baby without known risks for complications can participate. * Had the RSVpreF or Abrysvo vaccine during a previous pregnancy. * Had an ultrasound scan at 18 weeks or later during their current pregnancy, with no major fetal problems detected. * Based on their medical history, physical check-up, and the doctor's judgment, they are found suitable to join the study. * Agrees to let their baby take part in the study and gives their permission. * Able to sign a consent form, agreeing to follow the rules and conditions of the study. Key Exclusion Criteria * Received any approved or experimental RSV vaccine since their previous pregnancy. * Has a pre-pregnancy body mass index (BMI) over 40 kg/m2. * History of a severe bad reaction to a vaccine or a serious allergic reaction (like anaphylaxis) to any ingredient in the study vaccine or a similar vaccine. * Current pregnancy problems or issues at the time of giving consent. * Previous pregnancy issues or problems at the time of giving consent. * Women who are breastfeeding at the time of enrollment Infant Participants * Proof that the parent(s) or legal guardian(s) has signed and dated a consent form. * Parent(s) or legal guardian(s) must agree to attend scheduled visits and follow the study plan, including laboratory tests and other procedures. Nonpregnant Participants-Cohort…