A comparative study of respiratory syncytial virus (RSV) prophylaxis in premature infants within the Canadian Registry of Palivizumab (CARESS)

Abstract

We examined the dosing regimens, compliance, and outcomes of premature infants who received palivizumab within the Canadian Registry of Palivizumab (CARESS). Infants receiving ≥1 dose of palivizumab during the 2006-2011 respiratory syncytial virus (RSV) seasons were recruited across 30 sites. Respiratory illness events were captured monthly. Infants ≤32 completed weeks gestational age (GA) (Group 1) were compared to 33-35 completed weeks GA infants (Group 2) following prophylaxis. In total, 6,654 patients were analyzed (Group 1, n = 5,183; Group 2, n = 1,471). The mean GA was 29.9 ± 2.9 versus 34.2 ± 2.2 weeks for Groups 1 and 2, respectively. Group differences were significant (all p-values <0.05) for the following: proportion of males, Caucasians, siblings, multiple births, maternal smoking, smoking during pregnancy, household smokers, >5 household individuals, birth weight, and enrolment age. Overall, infants received 92.6 % of expected injections. Group 1 received significantly more injections, but a greater proportion of Group 2 received injections within recommended intervals. The hospitalization rates were similar for Groups 1 and 2 for respiratory illness (4.7 % vs. 3.7 %, p = 0.1) and RSV (1.5 % vs. 1.4 %, p = 0.3). Neither the time to first respiratory illness [hazard ratio = 0.9, 95 % confidence interval (CI) 0.7-1.2, p = 0.5] nor to first RSV hospitalization (hazard ratio = 1.3, 95 % CI 0.8-2.2, p = 0.3) were different. Compliance with RSV prophylaxis is high. Despite the higher number of palivizumab doses in infants ≤32 completed weeks GA, the two groups' respiratory illness and RSV-positive hospitalization rates were similar.

Fig. 1

Cox proportional hazard curves depicting the effect of group allocation on the time to hospitalization for respiratory illness (a) and respiratory syncytial virus (RSV)-positive infection (b), comparing infants of ≤32 completed weeks gestational age (GA; solid lines) and those of 33–35 completed weeks GA (dotted lines). Group allocation did not have an effect in either case [respiratory illness: hazard ratio = 0.9, 95 % confidence interval (CI) 0.70–1.2, p = 0.5; RSV-positive infection: hazard ratio = 1.3, 95 % CI 0.8–2.2, p = 0.3]

Fig. 2

Cox proportional hazard curves illustrating the number of risk factors that had a significant effect on the time to first RSV-positive hospitalization: having siblings, >5 individuals in the household, a history of atopy in the immediate family, and smoking in the household