This pivotal Phase 2b study will determine if MEDI8897 will be efficacious in reducing medically attended RSV-confirmed lower respiratory tract infections (LRTI) in healthy preterm infants entering their first RSV season. The population to be enrolled is healthy preterm infants born between 29 weeks 0 days and 34 weeks 6 days GA who would not receive RSV prophylaxis. A total of 1500 infants will be randomized 2:1 to receive either MEDI8897 or placebo. Participants will be followed for 360 days after dosing. Enrollment is planned at approximately 197 sites across the USA, Canada, Europe, and the Southern Hemisphere.