Effect of palivizumab prophylaxis in decreasing respiratory syncytial virus hospitalizations in premature infants

Background. Respiratory syncytial virus (RSV) is a major cause of hospitalization in preterm infants and infants with chronic lung disease (CLD). Palivizumab, a humanized monoclonal antibody, was approved in Europe in 1999 as prophylaxis against severe RSV-related respiratory illness. No multiple season data have been published on palivizumab effectiveness in European populations. Data collected during 4 years in Spain compared RSV hospitalization rates and risk factors in a cohort of palivizumab-prophylaxed and nonprophylaxed preterm infants. Methods. The first cohort was derived from 2 previous studies and included 1583 infants followed during 2 RSV seasons (1998 to 1999, 1999 to 2000) before palivizumab initiation in Spain. The second cohort included 1919 infants who received palivizumab prophylaxis for 2 subsequent respiratory seasons (2000 to 2001, 2001 to 2002). Both cohorts were preterm (less than or equal to532 weeks gestational age) and :56 months old at onset of RSV season. Results. The RSV hospitalization rate in the palivizumab-prophylaxed cohort was 3.95, and it was 13.25% in nonprophylaxed infants This 70% overall difference in RSV hospitalization was observed despite the palivizumab-prophylaxed group's lower gestational ages, more severe neonatal intensive care unit respiratory courses and higher incidence of CLD. Significant risk factors for RSV hospitalization in both cohorts included: lower gestational age; chronologic age <3 months at RSV season onset; school age siblings; and lower parental education. Nonprophylaxed children had a higher risk for RSV-related hospitalization than did prophylaxed patients (odds ratio, 3.86; 95% confidence interval, 2.83 to 5.25). Conclusion. Data from this study support the effectiveness of palivizumab in significantly modifying RSV-related hospitalizations in high risk preterm infants, with and without CLD, during two respiratory seasons.