RSV Prefusion F Protein-Based Maternal Vaccine—Preterm Birth and Other Outcomes

( N Engl J Med . 2024;390(11):1009–1021. doi: 10.1056/NEJMoa2305478) Maternal immunization could protect infants from respiratory syncytial virus (RSV). GlaxoSmithKline (GSK) developed an RSV subunit vaccine for maternal use called RSVPreF3-Mat. However, during a phase 3 trial (RSV MAT-009) initiated in 2020, an imbalance in preterm births was observed in the vaccine group compared with the placebo group. Consequently, enrollment and vaccination were stopped in February 2022, prompting further investigation. This article presents the primary efficacy and safety findings from the trial, along with exploratory analyses examining the preterm birth safety signal.