Palivizumab immunoprophylaxis effectiveness in children with cystic fibrosis.

BACKGROUND

Evidence on the effectiveness of respiratory syncytial virus (RSV) immunoprophylaxis with palivizumab in children with cystic fibrosis (CF) is lacking.

METHODS

We utilized Medicaid Extract files from 27 states from 1999 to 2006 linked to the National Cystic Fibrosis Registry to establish a cohort of children 0-2 years with CF diagnosis. Eligible children entered the cohort after CF diagnosis and after RSV season onset, and were followed until season end, second birthday, death, or hospitalizations for reasons other then the study outcome. Two outcomes were examined: hospitalization for RSV infections (RSV-ha), or hospitalization for acute respiratory infections (ARI-ha). Palivizumab exposure was defined based on pharmacy or procedure claims as current (claim date plus 30 days), former (day 31-60 after a claim), and no exposure (days before the first or >60 days after any claim). Both outcomes were examined in a Cox regression model, adjusting for RSV risk factors and CF severity via exposure propensity score.

RESULTS

The matched cohort included 1,974 infants (2,875 infant seasons), who experienced 32 RSV-ha and 212 ARI-ha (3.9 and 26.2/1,000 season months, respectively). Compared to periods of no use, the adjusted hazard ratio for current use was 0.57 (95% confidence interval [CI]: 0.20-1.60) for RSV-related hospitalization and 0.85 (95% CI: 0.59-1.21) for ARI-related hospitalization. Each month of increasing age reduced the ARI-ha by 5.8%.

CONCLUSION

RSV hospitalization incidence was low suggesting either little contribution of the virus to respiratory infections in patients with CF or lack of RSV testing. Unadjusted and adjusted RSV-hospitalization incidence rates suggested potentially positive effects of palivizumab, but results were inconclusive due to small event rates. Hospitalizations for acute respiratory illness with possible RSV contribution showed no association with palivizumab use, suggesting limited overall effect of palivizumab. Younger age greatly increased infection risk.