This is a randomized, observer-blind, placebo-controlled trial enrolling third-trimester pregnant women in the Northern and Southern hemispheres, for up to four consecutive RSV seasons in each hemisphere. The trial will enroll 4636 third-trimester pregnant subjects. Women in the third trimester of a singleton uncomplicated pregnancy and 18 to 40 years of age (inclusive) will be enrolled and randomized in a 1:1 ratio into one of two treatment groups, active or placebo, over approximately the three months prior to peak RSV season. After the first global season of enrollment, the randomization scheme will be changed to a 2:1 (active/placebo) ratio to enable more efficient accrual of the safety database.

All maternal subjects will receive a single intramuscular (IM) injection on Day 0 with the assigned test article, the RSV F vaccine or placebo. Study participation for maternal subjects will span approximately nine (9) months from the first dose, ending six (6) months post-delivery. Study follow-up for infant subjects who are consented will span approximately one (1) year post-delivery.

Results

The New England Journal of Medicine published the results of this study on July 30, 2020. 

Results: A total of 4636 women underwent randomization, and there were 4579 live births. During the first 90 days of life, the percentage of infants with RSV-associated, medically significant lower respiratory tract infection was 1.5% in the vaccine group and 2.4% in the placebo group (vaccine efficacy, 39.4%; 97.52% CI, -1.0 to 63.7; 95% CI, 5.3 to 61.2). The corresponding percentages for RSV-associated lower respiratory tract infection with severe hypoxemia were 0.5% and 1.0% (vaccine efficacy, 48.3%; 95% CI, -8.2 to 75.3), and the percentages for hospitalization for RSV-associated lower respiratory tract infection were 2.1% and 3.7% (vaccine efficacy, 44.4%; 95% CI, 19.6 to 61.5). Local injection-site reactions among the women were more common with vaccine than with placebo (40.7% vs. 9.9%), but the percentages of participants who had other adverse events were similar in the two groups.

Conclusions: RSV F protein nanoparticle vaccination in pregnant women did not meet the prespecified success criterion for efficacy against RSV-associated, medically significant lower respiratory tract infection in infants up to 90 days of life. The suggestion of a possible benefit with respect to other end-point events involving RSV-associated respiratory disease in infants warrants further study.