Pfizer Research Devlopment Brooklyn, NY, United States
Introduction: The safety evaluation of pregnant persons in clinical trials carries challenges, including assessment of 2 populations (the pregnant person and fetus as 1 individual before birth and the newborn after birth). We present the prelicensure safety evaluation in a Phase 3 study of a bivalent RSV prefusion F vaccine (RSVpreF) administered during pregnancy. Methods: To describe the safety and tolerability profile of RSVpreF, the following were evaluated during a randomized controlled trial (RCT): local and systemic reactions within 7 days after vaccination and adverse events (AEs) through 1 month after vaccination (Maternal), AEs through 1 month after birth (Infant), adverse events of special interest (AESIs) and serious AEs (SAEs) (Maternal and Infant), and newly diagnosed chronic medical conditions (NDCMCs) (Infant) throughout the study. AESIs were predefined as preterm delivery (Maternal); preterm birth, low birth weight, and developmental delay (Infant); and SARS-CoV-2 (Maternal and Infant). Results: For maternal participants, postvaccination local and systemic reactions were mild to moderate. AE profiles suggested no safety concerns. The number of preterm births was balanced in most countries enrolled, including those in high income countries. There was a numerical imbalance in late preterm infants in upper-middle-income countries. Infant mortality data appeared favorable for the RSVpreF group. Conclusion/Implications: Our Phase 3 study of RSVpreF showed a favorable safety profile for maternal and infant participants with a first-time characterization of some critical safety data points in a prospective vaccine study for infant efficacy. Postmarketing surveillance studies will continue monitoring the safety of RSVpreF.
