A Study to Determine the Safety and Efficacy of the RSV F Vaccine to Protect Infants Via Maternal Immunization

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 could enroll up to 8618 third-trimester pregnant subjects, of which 4,636 were actually enrolled. Women in the third trimester of a singleton uncomplicated low-risk pregnancy and 18 to 40 years of age (inclusive) were enrolled and randomized in a 1:1 ratio into one of two treatment groups, active or placebo, over approximately three months prior to peak RSV season in their locale. After the first global season of enrollment, the randomization scheme was changed to a 2:1 (active/placebo) ratio to enable a more efficient accrual of the safety database. All maternal subjects were to 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 spanned approximately nine (9) months from the first dose, ending six (6) months post-delivery. Study follow-up for live-born infant subjects spanned approximately one (1) year post-delivery.