Infants and young children with bronchopulmonary dysplasia (BPD) and/or a history of prematurity are at high risk for serious RSV disease. Previous studies have suggested that RSV-IGIV may effectively reduce this risk. A randomized double-blind, placebo-controlled trial (PREVENT) was conducted to define the efficacy and safety of monthly RSV-IGIV prophylaxis in premature/BPD patients. Between 11/15/94 and 12/22/94, 510 children were randomized (260 placebo, 250 RSV-IGIV) at 54 centers in the US. Mean age at enrollment was 5.8 months (range, 0.1-23.8 months); mean gestational age at birth was 28.5 weeks; 60% had BPD and an O2 requirement within 6 months of randomization. Children received monthly intravenous infusions of 750 mg/kg RSV-IGIV or placebo (albumin) during the RSV season. Approximately 95% of children completed the protocol and 85% received a full course of study agent(4 or 5 infusions). RSV-IGIV prophylaxis was associated with a 41% reduction in RSV hospitalization (35/260 placebo vs 20/250 RSV-IGIV, p=0.047); 53% reduction in total days of RSV hospitalization/100 children (129 placebo vs 60 RSV-IGIV, p=0.045); 60% reduction in RSV hospital days with increased O2 requirement/100 children (85 vs 34, p=0.007); and 54% reduction in RSV hospital days with a moderate/severe lower respiratory tract infection(106 vs 49, p=0.049). RSV-IGIV recipients also had a 38% reduction in hospitalization for any respiratory illness (69/260 vs 41/250, p=0.005) and a 46% reduction in total days of respiratory illness hospitalization per 100 children (317 vs 170, p=0.005). RSV-IGIV infusions were well tolerated, with a safety profile similar to other intravenous immunoglobulin preparations. Between 1-3% of children had significant adverse experiences attributable to the treatment (fluid complications, fever, acute reactions). RSV-IGIV was safe and effective for the prevention of serious RSV disease in high-risk children with BPD and/or a history of prematurity. Funded by MedImmune, Inc.