Safety surveillance of respiratory syncytial virus (RSV) vaccine among pregnant individuals: a real-world pharmacovigilance study using the Vaccine Adverse Event Reporting System.

Objectives: To describe the post-marketing safety profile of respiratory syncytial virus prefusion F (RSVpreF) vaccine among pregnant individuals.

Design: This study analysed adverse event (AE) reports submitted to the U.S. Food and Drug Administration's Vaccine Adverse Event Reporting System (VAERS) database following RSVpreF immunisation from 1 September 2023 to 23 February 2024.

Setting: VAERS, as a national spontaneous vaccine safety surveillance system, provides insights into the safety profile of the RSVpreF vaccine in a real-world setting.

Participants: Surveillance data included all AE reports submitted to VAERS in pregnant individuals following vaccination.

Exposure: Receipt of RSVpreF vaccine among pregnant individuals in the USA.

Primary and secondary outcome measures: Descriptive statistics were used to assess all AE reports with RSVpreF, including frequency, gestational age at vaccination, time to AE onset, reported outcomes and proportion of serious reports. Data mining techniques were employed to identify disproportionate reporting of RSVpreF-event pairs. Reports of preterm births were clinically reviewed.

Results: VAERS received 77 reports pertaining to RSVpreF vaccination in pregnant individuals, with 42 (54.55%) classified as serious. The most frequently reported non-pregnancy-specific AEs were headache, injection site erythema and injection site pain. For pregnancy-specific AEs, preterm birth was the most frequently reported (12.8%), followed by AE terms such as preterm premature rupture of membranes and caesarean section (each at 3.3%), and cervical dilatation, haemorrhage during pregnancy and uterine contractions during pregnancy (each at 1.4%). Our disproportionality analysis indicated signals for various AEs, particularly preterm birth, indicating that reports of preterm birth in conjunction with RSVpreF vaccination were observed more frequently than statistically expected. Most of the reported preterm births were moderate to late, occurring between 32 and less than 37 weeks of gestation. The median time from immunisation to the onset of preterm birth was 3 days, with two-thirds of cases reported within a week of vaccination.

Conclusions: The AEs reported to VAERS among pregnant individuals vaccinated with RSVpreF largely aligned with the safety profile observed in prelicensure studies; however, this analysis also highlights the previously observed safety signal for preterm birth. Active surveillance studies focusing on maternal and perinatal outcomes are needed to further evaluate this signal and guide future clinical recommendations.