Respiratory syncytial virus (RSV) vaccine in late pregnancy not linked to preterm birth

Women who receive vaccination against respiratory syncytial virus (RSV) during late pregnancy in order protect a newborn do not have an increased risk of preterm birth, researchers reported in JAMA Network Open on July 8, 2024.

“The real-world evidence provides an additional layer of confidence about the safety of this vaccine during pregnancy,” said author Moeun Son, MD, Associate Professor of Obstetrics and Gynecology at Cornell Medicine Medical in New York. “Randomized clinical trials don’t always emulate the populations we see in the clinical setting, but now we have data from multiple populations showing no increase in preterm birth risk.”

In August of 2023, the (USA) U.S. Food and Drug Administration approved the Abrysvo vaccine for women between 32 and 36 weeks of pregnancy. A month later, the CDC’s Advisory Committee on Immunization Practices recommended the vaccine for eligible pregnant women during RSV season, which lasts from, September to the end of January.

A single shot stimulates production of protective antibodies that transfer from mother to infant through the placenta.

The purpose of this retrospective observational cohort study was to evaluate the association between prenatal RSV vaccination status and perinatal outcomes in subjects who delivered during the vaccination season, September 22, 2023 to January 31, 2024.

The primary outcome was preterm birth (PTB), defined as less than 37 weeks’ gestation.

Of 2,973 pregnant subjects (median age of 34.9 years), 1,026 (34.5%) received prenatal RSVpreF/Abrysvo vaccination. Fifteen subjects inappropriately received the vaccine at 37 weeks’ gestation or later and were included in the nonvaccinated group.

The researchers found that there was not a significant statistical difference in preterm birth rates between vaccinated women (5.9 percent) and unvaccinated women (6.7 percent).

There were no significant differences between the groups in neonatal outcomes based on vaccination status. Such outcomes included hypertensive disorders of pregnancy (HDP), stillbirth, small-for–gestational age birth weight, neonatal intensive care unit (NICU) admission, neonatal respiratory distress with NICU admission, neonatal jaundice or hyperbilirubinemia, neonatal hypoglycemia, and neonatal sepsis.

The authors concluded, “In this cohort study of pregnant individuals who delivered at 32 weeks’ gestation or later, the RSVpreF vaccine was not associated with an increased risk of PTB [pre-term birth] and perinatal outcomes. These data support the safety of prenatal RSVpreF vaccination, but further investigation into the risk of HDP [hypertensive disorders of pregnancy] is warranted.