• Safety and tolerability of MEDI-524 and palivizumab as measured by [ Time Frame: through Study Day 120 for patients who receive 4 doses and Study Day 150 for patients who receive 5 doses of study drug ] [ Designated as safety issue: Yes ]
• Pharmacokinetics of MEDI-524 [ Time Frame: · Serum concentrations at each data collection visit will be summarized ] [ Designated as safety issue: Yes ]

• - Safety and tolerability of MEDI-524 and palivizumab as measured by:
• - Adverse events through Study Day 120 for patients who receive 4 doses and Study Day 150 for patients who receive 5 doses of study drug (including the occurrence of increased toxicity grade from baseline as determined by laboratory evaluations)
• - Serious adverse events through Study Day 120 for patients who receive 4 doses and Study Day 150 for patients who receive 5 doses of study drug
• - Pharmacokinetics of MEDI-524-Serum concentrations at each data collection visit will be summarized

The primary objective of this study is to determine the effect on immune reactivity to MEDI-524.

The primary objective of this study is to determine the effect on immune reactivity to MEDI-524 of monthly intramuscular (IM) doses of MEDI-524 of monthly intramuscular (IM) doses of MEDI-524 administered for a second season, in children who previously received MEDI-524 in protocol MI-CP104. The secondary objectives are to 1) describe the safety and tolerability of MEDI-524 administered for a second season; 2) describe the serum concentration of MEDI-524 administered for a second season.

Inclusion Criteria:

• Previous participation in MI-CP104 and received at least 3 injections of MEDI-524 in MI-CP104
• The child must be less than or equal to 24 months of age at time of entry into the study (child must be entered on or before their 24-month birthday)
• The child must be able to complete the follow-up visits through 3-4 months after last dose (total length of participation of 6-8 months)
• Written informed consent obtained from the patient's parent(s) or legal guardian

Exclusion Criteria:

• Be hospitalized
• Receiving chronic oxygen therapy or mechanical ventilation at the time of study entry (including continuous positive airway pressure [CPAP])
• Evidence of infection with hepatitis A, B, or C virus
• Known renal impairment, hepatic dysfunction, chronic seizure disorder, or immunodeficiency or HIV infection
• Suspected serious allergic or immune mediated events with prior receipt of MEDI-524
• Acute illness or progressive clinical disorder
• Active infection, including acute respiratory syncytial virus (RSV) infection at the time of enrollment
• Previous reaction to IGIV, blood products, or other foreign proteins
• Have ever received palivizumab
• Received within the past 120 days or currently receiving immunoglobulin products (such as RSV-IGIV [RespiGam(R)], IVIG), or any investigational agents (except MEDI-524)
• Currently participating in any investigational study