Objective To determine if RSV hospitalization (RSVH) rates in infants with or without palivizumab prophylaxis (PP) in their first RSV season differed in the subsequent respiratory season.

Methods This European and Canadian Phase IV, case-matched, cohort surveillance study compared the RSVH rates during the second respiratory season in preterm children with and without PP in their first year of life. Subjects were matched according to season, postmenstrual age; month of birth±3 months; and gender (if possible) and were followed over their second RSV season. Data were collected by interval medical and environmental questionnaires and review of medical records. 1368 enrolled subjects (684/group) were included in the primary analysis. As pre-specified, these study data were combined with data from 2 similar studies, for a total of 1844 subjects (972 palivizumab, 872 control) for primary analysis.

Results No statistically significant difference in the RSVH rates was observed between palivizumab (2.06%) and control (1.26%) groups. The one-sided 97.5% upper confidence bound for the difference in event rates was 1.96% using the normal approximation to the binomial distribution and 2.77% using an exact method. Each confidence bound was below the pre-specified non-inferiority margin of 3%, thus the palivizumab group demonstrated non-inferiority to the control group. No safety signals were detected in infants who had previously received PP in their first RSV season.

Conclusion Infants who receive palivizumab during their first year of life are not at increased risk for RSVH in the subsequent respiratory season.

Funded by Abbott.