Is the Maternal RSV Vaccine Safe? New Clinical Evidence

Respiratory syncytial virus (RSV) remains a leading cause of severe infant respiratory disease worldwide. Consequently, medical organizations recommend maternal immunization during the third trimester to protect newborns. However, clinicians often face questions regarding maternal RSV vaccine safety. A newly published real-world study provides reassuring evidence on this critical issue.

Evaluating Maternal RSV Vaccine Safety in Real-World Settings

To address these safety concerns, researchers conducted a target trial emulation study within the Vaccine Safety Datalink. Specifically, they analyzed electronic health records of pregnant patients aged 16 to 49 years. The study team analyzed patients receiving the bivalent prefusion F vaccine (RSVpreF) at 32 to 36 gestational weeks. Subsequently, they matched 13,966 vaccinated individuals 1:1 with unvaccinated pregnant peers. The matching process controlled for gestational week, site, and propensity to vaccinate. Therefore, this robust methodology minimized potential confounding factors.

Key Obstetric and Neonatal Outcomes

Importantly, the trial found no increased risk for several major adverse neonatal outcomes. For example, preterm birth rates did not differ significantly between the groups. Specifically, preterm birth occurred in 4.0% of vaccinated patients compared to 4.5% of unvaccinated matches. Additionally, the risk of stillbirth remained extremely low and similar across both cohorts. Furthermore, the investigators observed no significant difference in small-for-gestational-age birth weight rates. These reassuring findings suggest that maternal RSV vaccine safety holds strong for crucial infant health measures.

A Modest Association with Hypertensive Disorders

Although neonatal outcomes were highly favorable, the study did reveal a small safety signal. Specifically, the rate of any hypertensive disorder of pregnancy (HDP) was slightly higher in the vaccinated cohort. Indeed, HDP occurred in 17.3% of vaccinated patients versus 15.0% of their matched controls. This small difference was statistically significant. Because of this finding, clinicians should remain vigilant when monitoring pregnant patients. Nonetheless, the overall safety profile remains positive. Consequently, healthcare providers can confidently counsel patients on the overall benefits of maternal immunization.

Frequently Asked Questions

Q1: Does maternal RSV vaccination increase the risk of preterm birth?

No, the latest real-world surveillance data shows no increased risk of preterm birth following vaccination. Specifically, preterm birth rates were 4.0% in the vaccinated group and 4.5% in the unvaccinated group.

Q2: What adverse maternal outcomes are linked to the RSVpreF vaccine?

The study identified a small but statistically significant increase in the risk of hypertensive disorders of pregnancy. However, the rates of stillbirth and small-for-gestational-age infants did not differ significantly between vaccinated and unvaccinated individuals.

Q3: When should pregnant individuals receive the maternal RSV vaccine?

Medical guidelines recommend administering the vaccine between 32 and 36 weeks of gestation. Consequently, this timing helps optimize antibody transfer to the newborn while avoiding earlier risk windows.

References

1. DeSilva M et al. Association of Respiratory Syncytial Virus Vaccination During Pregnancy With Adverse Obstetric and Neonatal Outcomes. Obstet Gynecol. 2026 Jun 18. doi: 10.1097/AOG.0000000000006354. PMID: 42314184.
2. Son M et al. Nonadjuvanted Bivalent Respiratory Syncytial Virus Vaccination and Perinatal Outcomes. JAMA Netw Open. 2024;7(7):e2419268. doi: 10.1001/jamanetworkopen.2024.19268.
3. Kampmann B et al. Bivalent Prefusion F Vaccine in Pregnancy to Prevent RSV Illness in Infants. N Engl J Med. 2023 Apr 20;388(16):1451-1464. doi: 10.1056/NEJMoa2216480.