The purpose of this study is to measure the rate of anti-palivizumab antibodies (also referred to as immune reactivity or immunogenicity) in subjects receiving either the liquid or lyophilized formulation of palivizumab. This study will compare the number and percentage of subjects with anti-palivizumab antibodies receiving either the liquid or lyophilized formulation of palivizumab.

The approved liquid formulation of palivizumab was developed to simplify preparation of the drug before injection. Both formulations of palivizumab have been shown to be bioequivalent in children 6 months of age or younger with a history of chronic lung disease. In previous studies of liquid palivizumab, immunogenicity was evaluated up to 2 months after dosing in adults, and 1 month after dosing in children. In this study, MI-CP116, immunogenicity will be evaluated between 4 and 6 months after the last dose of study drug, in order to provide data at a time point significantly distant from dosing when drug interference is minimal.

• Biological: Lyophilized Palivizumab
• Biological: Liquid Palivizumab

• Active Comparator: Liquid Palivizumab
• Active Comparator: Lyophilized Palivizumab

Inclusion Criteria:

• Medically stable child with chronic lung disease of prematurity who is ≤24 months of age at randomization OR child with premature birth (gestational age ≤35 weeks or less) and who is 6 months of age or younger at randomization
• Written informed consent obtained from the patient's parent(s) or legal guardian(s)
• The child must be able to complete the follow-up visit 4-6 months after the last dose of study drug

Exclusion Criteria:

• Hospitalization at the time of randomization (unless discharge is anticipated within 3 weeks)
• Be receiving mechanical ventilation at the time of study entry (including CPAP)
• Congenital heart disease (children with uncomplicated CHD [e.g., PDA, small septal defect] and children with complicated CHD who are currently anatomically and hemodynamically normal can be enrolled).
• Mother with HIV infection (unless the child has been proven to be not infected)
• Life expectancy <6 months
• Known allergy to Ig products
• Acute respiratory or other acute infection or illness
• Previous reaction to IGIV, blood products, or other foreign proteins
• Receipt of lyophilized palivizumab, RSV-IG IV, or other RSV-specific monoclonal antibody, or any other polyclonal antibody (for example, Hepatitis B IG, IVIG, VZIG) within 3 months prior to randomization
• Any previous receipt of MEDI-524
• Participation in other investigational drug product studies