This study is a pivotal Phase 2/3 randomized, double-blind, palivizumab-controlled study to evaluate the safety, pharmacokinetics (PK), anti-drug antibody (ADA) response, and descriptive efficacy for MEDI8897 in high-risk infants eligible to receive palivizumab when entering their first or second RSV season (Season 1 or Season 2, respectively).

Approximately 1,500 palivizumab-eligible infants entering their first RSV season will be enrolled into one of 2 cohorts : (1) preterm cohort, including approximately 750 preterm infants (≤ 35 weeks GA) without CLD/CHD, or (2) CLD/CHD cohort, including approximately 750 infants with CLD of prematurity or hemodynamically significant CHD.

A minimum of 100 infants with hemodynamically significant CHD will be enrolled. Within each cohort, randomization will be stratified by hemisphere (northern, southern) and subject age at the time of Season 1 randomization (≤ 3 months, > 3 to ≤ 6 months, > 6 months).