Nonadjuvanted Bivalent RSV Vaccination Not Associated With Preterm Birth, Study Finds

No association was found between nonadjuvanted bivalent respiratory syncytial virus prefusion F (RSVpreF) protein subunit vaccination during pregnancy and preterm birth (PTB) in a retrospective observational cohort study published in JAMA Network Open.¹

The researchers believe the study supports the overall safety of prenatal RSVpreF vaccination.

"RSVpreF vaccination steadily increased throughout the 2023 to 2024 RSV season, with the largest increase seen after on-site vaccine availability,” wrote the researchers of the study. “In the main analyses, there were no significant differences in maternal or perinatal outcomes between patients who had EHR [electronic health record] evidence of prenatal RSVpreF vaccination and those who did not.”

In August 2023, RSVpreF became the first FDA-approved vaccine for use in pregnant individuals to prevent lower respiratory tract disease (LRTD) and severe LTRD caused by RSV in infants from birth through age 6 months.²

“RSV is a common cause of illness in children, and infants are among those at highest risk for severe disease, which can lead to hospitalization,” said Peter Marks, MD, PhD, director of the FDA’s Center for Biologics Evaluation and Research, in a statement. “This approval provides an option for health care providers and pregnant individuals to protect infants from this potentially life-threatening disease.”

However, clinical vaccine data are lacking, and this study aimed to evaluate the association between prenatal RSV vaccination and perinatal outcomes among patients who delivered during the 2023 to 2024 RSV vaccination season.

The study included patients who delivered at 32 0/7 weeks gestation or later at 2 New York City hospitals within 1 health care system from September 22, 2023, to January 31, 2024.¹ Patients with unknown gestational ages and those with multifetal gestations were excluded.

Using data from a research repository from electronic health records (EHRs), the researchers were able to link birthing parents and infant records, including recorded diagnoses, billing codes, as well as data on visits, medications, and laboratory and imaging results. Additionally, demographic information such as race and ethnicity were collected by self-reports during hospital visits.

The primary outcome was any birth occurring at less than 27 weeks’ gestation, and secondary pregnancy outcomes were hypertensive disorders of pregnancy (HDP), small-for-gestational age (SGA) birth weight, and stillbirth.

Secondary neonatal outcomes were neonatal intensive care unit (NICU) admission, respiratory distress with NICU admission, jaundice or hyperbilirubinemia, hypoglycemia, and sepsis.

A total of 2973 pregnant individuals were included in the study, in which 1026 (34.5%) received prenatal RSVpreF vaccination. However, 15 patients inappropriately received the vaccine at 37 weeks’ gestation or later and were designated to the unvaccinated cohort.

Of the patients who received the vaccine, 5.9% experienced prenatal outcomes compared with 131 (6.7%) who did not. After adjusting for potential confounders, RSVpreF was not associated an increased risk for PTB (adjusted HR, 0.93; 95% CI, 0.64-1.34). Additionally, no significant differences were identified in pregnancy and neonatal outcomes based on vaccination status in the logistic regression models, but increased risk of HDP in the time-dependent model was seen (HR, 1.43; 95% CI, 1.16-1.77).

However, the researchers acknowledged some limitations to the study. First, because the study was conducted in New York City, it may not be generalizable to other locations. Second, RSVpreF vaccination status was based on EHR records only, and it is possible some patients were misclassified as not having received vaccination when they did.

Despite these limitations, the researchers believe the study supports the overall safety of prenatal RSVpreF vaccination.

“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 and perinatal outcomes,” wrote the researchers. “These data support the safety of prenatal RSVpreF vaccination, but further investigation into the risk of HDP is warranted.”

References

1. Son M, Riley LE, Staniczenko AP, et al. Nonadjuvanted bivalent respiratory syncytial virus vaccination and perinatal outcomes. JAMA Netw Open. Published online July 1, 2024. doi:10.1001/jamanetworkopen.2024.19268

2. FDA approves first vaccine for pregnant individuals to rrevent RSV in infants. News release. August 21, 2023. Accessed July 12, 2024. https://www.fda.gov/news-events/press-announcements/fda-approves-first-vaccine-pregnant-individuals-prevent-rsv-infants