Originally published by 2 Minute Medicine^® (view original article). Reused on AccessMedicine with permission.

1. In this randomized controlled trial, respiratory syncytial virus prefusion F protein−based vaccine (RSVpreF) administered during pregnancy prevented severe RSV respiratory tract illness in infants.

2. When administered during pregnancy, there were no safety concerns identified with the RSVpreF vaccine.

Evidence Rating Level: 1 (Excellent)

Study Rundown:

RSV is a common cause of acute lower respiratory tract illness and a leading cause of death in infants younger than six months of age, particularly in low- and middle-income countries. Maternal vaccination has been shown to provide protection in infants immediately after birth and during the first months of life. However, there is a gap in knowledge as to whether RSVpreF administered during the late second or third trimester of pregnancy may protect infants from severe RSV illness during the first few months of life. Overall, this study found that the RSVpreF vaccine had a favorable safety profile and was effective against severe RSV-associated lower respiratory tract illness and RSV associated hospitalization in infants through six months of age. This study was limited by the exclusion of women with high-risk pregnancies, such as those with high current risk of preterm birth, multiple pregnancy, or a previous infant with a clinically significant congenital anomaly. Nevertheless, these study’s findings are significant, as they demonstrate that the RSVpreF vaccine is safe and effective against severe RSV associated lower respiratory tract illness in infants and those less than six months of age.

Click to read the study in NEJM

Relevant Reading: Vaccine Efficacy in Adults in a Respiratory Syncytial Virus Challenge Study

In-Depth [randomized controlled trial]:

This phase three, double-blind, randomized, placebo-controlled trial was conducted in 18 countries over four RSV seasons. Patients were healthy women who were 49 years of age or younger at 24 to 36 weeks’ gestation on the day of planned injection, with an uncomplicated, singleton pregnancy and no known increased risk of pregnancy complications. Patients who had high-risk pregnancies, multiple pregnancies, or had a prior infant with a clinically significant congenital anomaly were excluded from the study. The primary outcomes measured were medically attended severe RSV-associated lower respiratory tract illness and medically attended RSV associated lower respiratory tract illness in infants within 90, 120, 150, and 180 days after birth. Outcomes in the primary analysis were assessed via an alpha-spending function and a Bonferroni procedure. Based on the primary analysis, medically attended severe lower respiratory tract illness occurred within 90 days after birth in six infants of women in the vaccine group and 33 infants of women in the placebo group (vaccine efficacy, 81.8%; 99.5% Confidence Interval [CI], 40.6 to 96.3); 19 cases and 62 cases, respectively, occurred within 180 days after birth (vaccine efficacy, 69.4%; 97.58% CI, 44.3 to 84.1). Though the results did not meet statistical success criterion, medically attended RSV-associated lower respiratory tract illness occurred within 90 days after birth in 24 infants of women in the vaccine group and 56 infants of women in the placebo group (vaccine efficacy, 57.1%; 99.5% CI, 14.7 to 79.8). In summary, this study demonstrates that RSVpreF vaccine was effective against severe RSV associated lower respiratory tract illness in infants with no safety concerns identified.

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