Study confirms Pfizer’s Abrysvo vaccine safety for pregnant women against RSV

USA — In a new study published in JAMA Network Open, researchers have discovered reassuring data regarding the safety of Pfizer’s Abrysvo vaccine against respiratory syncytial virus (RSV) in pregnant women.

Based on real-world data, the study resolves previous clinical trial concerns about the vaccine’s possible risk of pre-term or early babies.

Abrysvo, which was licensed by the FDA last year for pregnant women in their second or third trimesters, seeks to protect newborns from RSV infections during the first six months after delivery.

Initial clinical trials raised concerns since vaccinated participants had a higher rate of preterm deliveries than those who got a placebo.

However, this retrospective analysis included women between 24 and 36 weeks of pregnancy and discovered no significant changes in the incidence of small-for-gestational-age babies or stillbirths between the vaccinated and unvaccinated groups.

Notably, the study found an elevated risk of overall hypertension issues during pregnancy in those who received the RSV vaccine, according to a time-dependent model.

The study, which ran from September 2023 to January 2024 at two large hospitals in New York City, examined the electronic health records of 1,026 vaccinated and 1,947 unvaccinated individuals.

Preterm births occurred in 5.9% of the vaccinated cohort, slightly fewer than in the unvaccinated group (6.7%).

Lead author Moeun Son, MD, an associate professor of obstetrics and gynecology at Weill Cornell Medicine, emphasized the importance of real-world evidence in increasing trust in the vaccine’s safety during pregnancy.

He emphasized that, while randomized clinical trials may not always fully reflect real-world diversity, the study presents strong evidence across varied communities that show no higher risk of pre-term births associated with the immunization.

Annette Regan, PhD, MPH, from the University of San Francisco, stated in an accompanying editorial that these findings would reassure doctors and expecting women about the vaccine’s safety profile.

The reassurance comes after phase 3 clinical trials revealed a slightly greater rate of pre-term deliveries in the intervention arm than in the control arm.

RSV continues to be a major concern, accounting for roughly 80,000 hospitalisations and up to 300 deaths among children under the age of five in the United States each year.

The Centres for Disease Control and Prevention (CDC) consequently recommends that pregnant women receive a single dose of the RSV vaccination between September and January to protect their infants against this potentially severe respiratory virus.

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