21 Apr 2023 • Introduction Respiratory syncytial virus (RSV) is a common respiratory infection that can cause severe illness in infants. It is unclear whether vaccination during pregnancy can reduce the burden of RSV-associated lower respiratory tract illness in newborns and infants.

Method In this phase 3, double-blind trial, pregnant women at 24 through 36 weeks’ gestation were randomly assigned to receive a single injection of a bivalent RSV prefusion F protein-based vaccine or placebo. The study was conducted in 18 countries and included 7,258 participants.

Results At the prespecified interim analysis, the vaccine efficacy met the success criterion for one of the primary endpoints. Medically attended severe lower respiratory tract illness occurred in fewer infants of women in the vaccine group than in the placebo group within 90 days after birth (6 vs. 33 infants, respectively) and within 180 days after birth (19 vs. 62 infants, respectively). Vaccine efficacy was 81.8% and 69.4%, respectively, for these endpoints. However, vaccine efficacy for medically attended RSV-associated lower respiratory tract illness within 90 days after birth did not meet the statistical success criterion.

Conclusion The RSV vaccine administered during pregnancy was effective against medically attended severe RSV-associated lower respiratory tract illness in infants, and no safety concerns were identified.

Source: NEJM | Read full story