Study finds Pfizer's RSV vaccine not tied to higher risk of pre-term births

By Christy Santhosh

(Reuters) - Pfizer's respiratory syncytial virus (RSV) vaccine for pregnant women was not tied to a higher risk of pre-term or early births, according to a study published on Monday that analyzed real-world use of the shots.

The vaccine Abrysvo was approved by the U.S. Food and Drug Administration last year for women in their second or third trimesters of pregnancy to prevent infections tied to RSV in babies in the first six months after birth.

However, some experts had raised concerns over a higher number of pre-term births among participants taking the Pfizer shot compared to those who received a placebo in the company's clinical trial.

Researchers from Weill Cornell Medical College in New York conducted the retrospective study in women who were 24 to 36 weeks into pregnancy, and found no significant statistical difference between the vaccinated women's pre-term birth rate of 5.9% compared with unvaccinated women's 6.7%.

Health regulators however recommended a narrower gestational window, said Annette Regan, from the University of San Francisco's School of Nursing and Health Professions, in an editorial accompanying the study.

"Despite the need for further research and surveillance, results from this study should offer initial reassurance to regulators, policymakers, health care professionals, and pregnant patients," Regan wrote in the article published in JAMA.

In most of the continental U.S., the Centers for Disease Control and Prevention (CDC) and the Advisory Committee on Immunization Practices (ACIP) recommend the vaccine for women who are 32 to 36 weeks pregnant between September and January.

The study analyzed electronic health records of women across two New York City hospitals who gave birth between September last year to late January.

RSV leads to the hospitalization of about 58,000 to 80,000 children younger than 5 years annually.

Pfizer's vaccine is the only maternal RSV shot approved in the US. The vaccine, along with rivals by GSK and Moderna, is also approved for older adults.

(Reporting by Christy Santhosh in Bengaluru; Editing by Vijay Kishore)