Title: PREVENTION OF INFANT RSV ILLNESS WITH AN RSVpreF VACCINE IN PREGNANCY

INTRODUCTION
RSV is the leading cause of lower respiratory tract illnesses worldwide, with a substantial burden of disease borne to young infants, particularly those in lower- and middle-income countries. Rates of severe RSV illness are highest in infants less than 6 months of age, with a peak in hospitalization between 1 and 2 months of life. Treatment of RSV disease for infants consists primarily of supportive care, as there is no vaccine available to prevent RSV disease in infants. Maternal immunization to protect infants early in life offers an attractive strategy for infant disease prevention in this population.

Pfizer’s RSVpreF bivalent vaccine is a prophylactic vaccine that is being investigated for the prevention of medically attended lower respiratory tract disease (MA-LRTI) and severe medically attended lower respiratory tract disease (sMA-LRTI) caused by RSV in infants from birth through 6 months of age by active immunization of pregnant maternal participants in a Phase 3 trial. Here we present results of our primary analysis. 

METHOD

Study C3671008 is an ongoing Phase 3, multicenter, randomized, double-blinded, placebo-controlled study executed in 18 countries.
7,392 maternal participants randomized 1:1 RSVpreF 120µg or placebo
Pregnant participants ≤49 years of age between ≥24 and ≤36 weeks gestation
Follow-up 6 months postpartum
7,128 infants born to vaccinated mothers

CONCLUSION

RSVpreF maternal immunization demonstrated a satisfactory safety profile in mothers and their infants.

RSVpreF vaccine elicited high and consistent vaccine efficacy (VE) against severe infant MA-LRTI of 81.8% at 90 days and 69.4% at 180.

Success criterion was not met for MA-LRTI endpoint (57.1% VE at 90 days), however clinically meaningful efficacy was observed with VE of 51.3% out to 180 days.

Our secondary endpoint of persistent VE against severe RSV to 360 days was met (40-45%).

Protection against hospitalizations due to RSV after 6-months post-birth was also demonstrated at 67.7

ACKNOWLEDGMENTS
The Matisse team would like to thank the clinical trial participants and their families, sites, investigators and their dedicated staff, our clinical trial CRO and other partners, governments and regulatory authorities, and colleagues at Pfizer.