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Vaccines

1D-05 - Rapid Surveillance Study to Evaluate Safety of Respiratory Syncytial Virus (RSV) Vaccine (ABRYSVO™) Exposure During Pregnancy in the United States

Sunday, August 24, 2025
11:30 AM - 11:45 AM ET
Background: ABRYSVO™ is a maternal vaccine approved to prevent infant RSV-associated lower respiratory tract disease. A rapid cycle analysis is monitoring ABRYSVO safety (EUPAS1000000115). Cumulative data through 3 of 5 planned hypothesis tests are presented.

Objectives: To rapidly monitor incidence proportions [IP] of 10 prespecified safety outcomes following ABRYSVO or comparator vaccine among privately insured pregnant patients aged 15-54 years in US healthcare claims data.

Methods: Pregnancies vaccinated at 32-36 weeks gestation with ABRYSVO (exposure) or influenza/Tdap/COVID-19 (comparator) were identified from Sep 2018-Jan 2023 (historical comparator) and Sep 2023-May 2024 (exposure, concurrent comparator) from 5 national/regional insurers. When possible, outcome IPs were assessed using maximized Sequential Probability Ratio Tests designed with 90% power to rule out various relative risks (RR) by the 5th test: preterm birth [PTB] (RR=1.20 in historical; RR=1.25 in concurrent comparison), hypertensive disorders of pregnancy [HDP] (1.10; 1.10), stillbirth (3.25; 3.25), premature labor without preterm delivery [PTL] (1.30; 1.35), premature rupture of membranes [PROM] (1.10; 1.10), preterm PROM [PPROM] (1.20; 1.25), small for gestational age [SGA] (1.50; 1.75), large for gestational age [LGA] (1.35; 1.50), and low birth weight [LBW] (2.00; 2.50). Stratification covariates included maternal age, season, gestational age at vaccination, and evidence of high-risk for PTB.

Results: The ABRYSVO cohort tended to be older, vaccinated later, at high risk, and have more immunocompromising conditions.
Historical Comparison: 11,457 ABRYSVO and 143,459 comparator pregnancies were included. PTB, PTL, SGA, LGA, and LBW reached a statistical stopping point, ruling out RRs greater than noted above. HDP (crude IP 17.3% [95% confidence interval [CI]: 16.6-18.0%] vs. 13.4% [13.2-13.6%]), PROM (14.1% [13.5-14.8%] vs. 12.5% [12.4-12.7%]), and PPROM (3.6% [3.2-3.9%] vs. 3.0% [2.9-3.1%]) met criteria to reject the null hypothesis of RR no greater than noted.
Concurrent Comparison: Among 11,458 ABRYSVO and 9,472 comparator pregnancies, HDP (17.3% [95% CI: 16.6-18.0%] vs. 15.1% [14.4-15.9%]) and PROM (14.1% [13.5-14.8%] vs. 13.1% [12.4-13.7%]) met criteria to reject the null hypothesis of RR no greater than noted.
For both comparisons, monitoring is ongoing for Guillain-Barré Syndrome and outcomes that have not reached statistical stopping points.

Conclusions: This interim analysis found no increased risk of PTB in the historical comparison. Statistically elevated relative risks in HDP, PROM, and PPROM require further analysis with improved confounding control. Despite limitations, RCAs are important tools for ongoing rapid monitoring of vaccine safety.