Safety monitoring of Pfizer's Respiratory Syncytial Virus Vaccine in pregnant women in the Vaccine Adverse Event Reporting System (VAERS), 2023-2024, United States.

BACKGROUND

In September 2023, the Advisory Committee on Immunization Practices and the Centers for Disease Control and Prevention (CDC) recommended Pfizer's Respiratory Syncytial Virus (RSV) vaccine for pregnant women at 32-36 weeks' gestation using seasonal administration to prevent RSV-associated lower respiratory tract disease (LRTD) in infants aged <6 months. In clinical trials among pregnant women at 24-36 weeks' gestation, more preterm births and hypertensive disorders of pregnancy were noted among Pfizer's RSV vaccine recipients compared with placebo, but the differences were not statistically significant. Post-licensure safety monitoring of the Pfizer RSV vaccine in pregnant women is important to help inform immunization policies.

OBJECTIVE

We assessed reports after Pfizer's RSV Vaccine in pregnant women submitted in the Vaccine Adverse Event Reporting System (VAERS), a passive surveillance system.

METHODS

We searched VAERS for U.S. reports of adverse events (AEs) or vaccination errors in pregnant women vaccinated with the Pfizer RSV vaccine. We analyzed reports received from August 20, 2023 through June 3, 2024. Clinicians reviewed reports and available medical records.

RESULTS

VAERS received 121 reports of pregnant women who received the Pfizer RSV vaccines. Injection site and systemic reactions were described in 44 (36 %) reports. The most commonly reported pregnancy-specific outcomes were preterm birth in 37 (31 %) and hypertensive disorders of pregnancy in 9 (7 %).

CONCLUSIONS

During the first U.S. RSV season in which the Pfizer RSV vaccine was approved and recommended for use during pregnancy, the types of AEs reported were consistent with prelicensure studies. Preterm birth was described commonly in the reports. Studies assessing potential association between Pfizer's maternal RSV vaccine and preterm birth are ongoing. CDC and Food and Drug Administration (FDA) will continue to monitor the safety of this vaccine in future seasons.