Abstract 993 Poster Session IV, Tuesday, 5/4 (poster 86)

The IMpact-RSV study demonstrated that palivizumab (Synagis™) is safe and effective for prevention of serious RSV disease in high risk children. Repeated dosing of this humanized monoclonal during a single RSV season was not associated with the development of anti- palivizumab antibodies. In this study, 88 children who participated in the IMpact-RSV trial at 6 centers and had received either palivizumab or placebo (2:1 randomization) received palivizumab (15 mg/kg IM q30 days × 5) in the subsequent RSV season to assess the development of antibodies upon re-exposure. Blinding of the original treatment assignment from IMpact-RSV for these sites was maintained until the end on this trial.

Thirty two (36%) children had received placebo on IMpact-RSV and received palivizumab for the first time in this study; 56 (64%) had received palivizumab previously and thus received palivizumab for a second consecutive season. Adverse events (AEs), immunogenicity, urinalysis, AST/ALT, BUN/Cr, and PK were assessed. Baseline demographics were similar in the groups; mean age at entry was 16 months, approximately 20% had bronchopulmonary dysplasia. Eighty-seven (99%) received all 5 injections. Palivizumab was safe and well tolerated in both groups. No local or systemic reactions suggestive of a possible immune mediated response were reported. The pattern and type of AEs were generally those expected in this population. AEs were not significantly different, except for teething pain and otitis media, which were reported somewhat more frequently in the second season children. Only 7 (8%) of patients reported AEs judged related to palivizumab; 3 (9%) first season patients and 4 (7%) second season patients. One patient had transient low level titers (1:160) measured in the palivizumab immunogenicity assay; not temporally associated with AEs or change in PK. Neither of two patients with low level titers in IMpact-RSV had measurable titers during this trial. Palivizumab levels were similar to those measured in previous trials. Administration of 15 mg/kg of palivizumab IM monthly to high risk infants during a second season was safe and well tolerated.

Funded by MedImmune, Inc.