Maternal RSV Vaccination Not Associated With Increased Preterm Birth Risk


Current recommendations suggest women receive the RSV vaccine between 32 and 36 weeks' gestational age.

Vaccination with Abrysvo, Pfizer’s nonadjuvanted bivalent respiratory syncytial virus (RSV) prefusion F (RSVpreF) protein subunit vaccine, was not associated with an increased risk of preterm birth among pregnant individuals who received the vaccine, according to research results published in JAMA Network Open.

Current recommendations, endorsed by major obstetric professional organizations in the US, suggest that most pregnant individuals should be vaccinated between 32- and 36-weeks’ gestation. However, investigators noted, “clinical data from the US 2023 to 2024 RSV season are currently lacking,” and the current study aimed to examine vaccine uptake among a diverse population of pregnant individuals.

Researchers conducted a retrospective, observational cohort study of patients who gave birth at 2 New York City hospitals between September 22, 2023, and January 31, 2024. The primary study outcome was preterm birth, defined as any birth occurring at less than 37 weeks’ gestation; secondary pregnancy outcomes included hypertensive disorders of pregnancy such as gestational hypertension, preeclampsia, and eclampsia, small-for-gestational age birthweight, and stillbirth, and secondary neonatal outcomes included neonatal intensive care unit (NICU) admission, respiratory distress with NICU admission, jaundice or hyperbilirubinemia, hypoglycemia, and sepsis.

Current recommendations suggest women receive the RSV vaccine between 32 and 36 weeks' gestational age. | Image credit: Marina Demidiuk -

Current recommendations suggest women receive the RSV vaccine between 32 and 36 weeks' gestational age. | Image credit: Marina Demidiuk -

The study cohort included a total of 2973 eligible individuals (median age, 34.9 years; IQR, 32.4-37.7 years), 56.7% of whom were White. A total of 34.5% of the cohort had electronic health record-documented evidence of receiving RSVpreF vaccination before delivery; 65.5% did not. Mean gestational age at vaccination was 34.5±1.4 weeks.

Overall, patients in the vaccinated group were slightly older (35.5 vs 34.6 years), and more patients in both groups had private insurance compared with Medicare or Medicaid. Individuals in the vaccination group were also more likely to be nulliparous and to have pregnancy via in vitro fertilization.

Preterm birth was noted in 6.5% of the total cohort, representing just 191 of 2973 patients, and vaccination during pregnancy was not significantly associated with an increased risk for preterm birth (OR, 0.88; 95% CI, 0.64-1.20). These rates “remained unchanged” following multivariable analyses (adjusted OR, 0.87; 95% CI, 0.62-1.20) and time-dependent covariate Cox regression model (HR, 0.93; 95% CI, 0.64-1.34). Both groups experienced more instances of spontaneous preterm birth, defined as birth after preterm labor or preterm premature membrane rupture, than nonspontaneous preterm birth: 63.3% vs 36.7% in the vaccinated group and 52.7% vs 47.3% in the unvaccinated group.

No significant differences in small-for-gestational age birthweight or stillbirth were noted. Results of a time-dependent model showed an increased overall risk of hypertensive disorders of pregnancy with RSVpreF vaccination (HR, 1.43; 95% CI, 1.16-1.77); stratified analyses showed differences for risks of both conditions based on insurance type and hospital site.

READ MORE: Pfizer Announces Positive Top-Line Data for Abrysvo Immunization in Adults Aged 18 to 59 Years

No significant differences in outcomes were noted in the newborns.

In the current study, researchers noted significant differences in self-identified race and ethnicity based vs vaccination status. “We found a significantly lower vaccination frequency among patients who self-identified as Black or Hispanic and those with government insurance,” they wrote, adding that these disparities are similar to those for other recommended prenatal vaccines, such as influenza, COVID-19, and tetanus-diphtheria-pertussis.

Study limitations include a lack of generalizability of results to areas outside of New York City, potential lack of capture of RSVpreF vaccinations performed at smaller pharmacies or clinics, and a “residual risk of immortal time bias” for preterm birth outcomes.

“These data add to the existing evidence supporting the overall safety of prenatal RSVpreF vaccination,” the researchers wrote, noting that the associations with risk of hypertensive disorders of pregnancy and small for gestational age birth weight should be “investigated further.”

“Prenatal RSVpreF vaccination remains underutilized,” they concluded, “and exploration of the factors and disparities associated with prenatal vaccination is needed.”

READ MORE: Immunization Resource Center

Son M, Riley LE, Staniczenko AP, et al. Nonadjuvanted bivalent respiratory syncytial virus vaccination and perinatal outcomes. JAMA Netw Open. 2024;7(7):e2419268. doi:10.1001/jamanetworkopen.2024.19268
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