The phase 3 MATernal Immunization Study for Safety and Efficacy, or MATISSE, demonstrated that a bivalent RSV prefusion vaccine candidate successfully protected newborns against severe RSV-related respiratory illness, according to a press release. The pre-planned interim efficacy analysis met the success criterion for one of two primary endpoints, showing that the observed efficacy for severe medically attended lower respiratory tract illness (severe MA-LRTI) was 81.8% in the first 90 days of life. The results also showed a substantial efficacy of 69.4% for infants in a 6-month follow-up period. While the statistical success criterion was not met for the second primary endpoint, clinically meaningful efficacy was seen for MA-LRTI (57.1%) among infants from birth through 90 days, and an efficacy for MA-LRTI of 51.3% was seen in the 6-month follow-up period. The vaccine was well tolerated, with no safety concerns. If approved by regulatory agencies, the vaccine would be the first maternal vaccine intended to prevent RSV among young infants, according to the press release.