Partial palivizumab prophylaxis and increased risk of hospitalization due to respiratory syncytial virus in a medicaid population: A retrospective cohort analysis

Abstract

Background: Infection with respiratory syncytial virus (RSV) is common among young children insured throughMedicaid in the United States. Complete and timely dosing with palivizumab is associated with lower risk ofRSV-related hospitalizations, but up to 60% of infants who receive palivizumab in Medicaid population do notreceive full prophylaxis. The purpose of this study was to evaluate the association of partial palivizumab prophylaxiswith the risk of RSV hospitalization among high-risk Medicaid-insured infants.Methods: Claims data from 12 states during 6 RSV seasons (October 1st to April 3th in the first year of life in 2003-2009)were analyzed. Inclusion criteria were birth hospital discharge before October 1st, continuous insurance eligibility frombirth through April 30th, ≥ one palivizumab administration from August 1st to end of season, and high-risk status(≥34 weeks gestational age or chronic lung disease of prematurity [CLDP] or hemodynamically significant congenitalheart disease [CHD]). Fully prophylaxed infants received the first palivizumab dose by November 30th with nogaps >35 days up to the first RSV-related hospitalization or end of follow-up. All other infants were categorizedas partially prophylaxed.Results: Of the 8,443 high-risk infants evaluated, 67% (5,615) received partial prophylaxis. Partially prophylaxedinfants were more likely to have RSV-related hospitalization than fully prophylaxed infants (11.7% versus 7.9%,p< 0.001). RSV-related hospitalization rates ranged from 8.5% to 24.8% in premature, CHD, and CLDP infants with partialprophylaxis. After adjusting for potential confounders, logistic regression showed that partially prophylaxed infants hada 21% greater odds of hospitalization compared with fully prophylaxed infants (odds ratio 1.21, 95% confidence interval1.09-1.34).Conclusions: RSV-related hospitalization rates were significantly higher in high-risk Medicaid infants with partialpalivizumab prophylaxis compared with fully prophylaxed infants. These findings suggest that reduced and/or delayeddosing is less effective.