GSK and Pfizer RSV Vaccines for Pregnant Women Increased Risk of Preterm Births — GSK Ended Its Trials, but FDA Approved Pfizer Shots

GSK on Thursday provided more details on the clinical trials for its maternal respiratory syncytial virus (RSV) vaccine. The company halted the trials and stopped developing the vaccine in February 2022, after identifying an increased risk of preterm birth among vaccinated mothers.

The details, published in a peer-reviewed article in the New England Journal of Medicine (NEJM), came after GSK previously reported the increased risk and subsequent termination of the trials to regulators, GSK’s investors and in the press.

According to the NEJM article, GSK was unable to identify a mechanism by which the vaccine caused the preterm births. However, the company also couldn’t identify any causes other than the vaccine being investigated.

Although GSK ended its trials due to the preterm birth safety signal, the U.S. Food and Drug Administration (FDA) in 2023 approved Pfizer’s RSV vaccine for pregnant women, — even though Pfizer also reported elevated rates of preterm birth among vaccinated women during clinical trials for the vaccine, Abrysvo.