Phase II, Double-blind, two-period, cross-over study to be conducted at 20 sites the U.S. A total of 150 children who meet the entry criteria will be randomized 1:1 to receive one of the following treatment sequence: Sequence A (single dose of the liquid formulation on Study Day 0 and a single dose of the lyophilized formulation on Study Day 30) or Sequence B (single dose of the lyophized forumation on Study Day 0 and single dose of the liquid formulation on Study Day 30). Children will be followed for adverse events through 30 days after each injection of study drug and will have blood collected for determination of palivizumab concentrations in serum.
A total of 150 children who meet the entry criteria will be randomized 1:1 to receive one of the following treatment sequence A or B.