Effectiveness of Respiratory Syncytial Virus Immunoprophylaxis in Reducing Bronchiolitis Hospitalizations Among High-Risk Infants

Abstract

We sought to determine the real-world effectiveness of respiratory syncytial virus (RSV) immunoprophylaxis in a population-based cohort to inform policy. The study population included infants born during 1996-2008 and enrolled in the Kaiser Permanente Northern California integrated health-care delivery system. During the RSV season (November-March), the date of RSV immunoprophylaxis administration and the following 30 days were defined as RSV immunoprophylaxis protected period(s), and all other days were defined as unprotected period(s). Numbers of bronchiolitis hospitalizations were determined using International Classification of Diseases, Ninth Revision, codes during RSV season. We used a proportional hazards model to estimate risk of bronchiolitis hospitalization when comparing infants' protected period(s) with unprotected period(s). Infants who had ever received RSV immunoprophylaxis had a 32% decreased risk of bronchiolitis hospitalization (adjusted hazard ratio = 0.68, 95% confidence interval: 0.46, 1.00) when protected periods were compared with unprotected periods. Infants with chronic lung disease (CLD) had a 52% decreased risk of bronchiolitis hospitalization (adjusted hazard ratio = 0.48, 95% confidence interval: 0.25, 0.94) when protected periods were compared with unprotected periods. Under the new 2014 American Academy of Pediatrics (AAP) guidelines, 48% of infants eligible for RSV immunoprophylaxis on the basis of AAP guidelines in place at birth would no longer be eligible, but nearly all infants with CLD would remain eligible. RSV immunoprophylaxis is effective in decreasing hospitalization. This association is greatest for infants with CLD, a group still recommended for receipt of RSV immunoprophylaxis under the new AAP guidelines.

Figure 1.

Distribution of the study population according to eligibility for and receipt of respiratory syncytial virus (RSV) immunoprophylaxis, Kaiser Permanente Northern California, 1996–2008. AAP, American Academy of Pediatrics; CLD, chronic lung disease.

Figure 2.

Data-processing strategy for creating analysis records during each infant’s first 5-month respiratory syncytial virus (RSV) season following birth, Kaiser Permanente Northern California, 1996–2008. The start of follow-up was the first day on which infants were eligible for RSV immunoprophylaxis based on American Academy of Pediatrics guidelines, the first day after birth hospitalization discharge, or the start of the RSV season (November 1), whichever came last. The end of follow-up was the last day on which infants were eligible for RSV immunoprophylaxis, the infant’s first birthday, or the end of the RSV season (March 31), whichever came first. Circles denote bronchiolitis hospitalization, and diamonds denote administration of RSV immunoprophylaxis.