Background: The incidence of and mortality from invasive pneumococcal disease are significantly higher in children with sickle cell disease than in the general pediatric population. The objective of this population-based study was to assess the effect of pneumococcal conjugate vaccine on rates of invasive pneumococcal disease among children with sickle cell disease.
Patients and methods: Records, including the history of pneumococcal conjugate vaccine administration, of 1247 children born after 1983 residing in metropolitan Atlanta, Georgia, with confirmed hemoglobinopathies were linked to an active surveillance database for invasive pneumococcal disease for the period of January 1, 1995, through January 1, 2003. The incidence of invasive pneumococcal disease and the percentage of rate reduction were estimated before and after pneumococcal conjugate vaccine licensure. Survival analysis was used to estimate the effect of pneumococcal conjugate vaccine on invasive pneumococcal disease rates while accounting for herd immunity.
Results: A significant decline in invasive pneumococcal disease in children with sickle cell disease < or = 10 years of age was noted after pneumococcal conjugate vaccine licensure, from 1.7 infections per 100 person-years (1995-2000) to 0.5 infections per 100 person-years (2001-2002), which represents a 68% reduction. The effectiveness of > or = 1 dose of pneumococcal conjugate vaccine was estimated by crude analysis to be 84.5% and by stratified survival analysis to be 81.4% when controlling for the presence of herd immunity in the 2 years after pneumococcal conjugate vaccine licensure. Serotype 6A invasive pneumococcal disease represented 36% of invasive pneumococcal disease before pneumococcal conjugate vaccine licensure and 0% after pneumococcal conjugate vaccine licensure, suggesting a protective effect against this pneumococcal conjugate vaccine-related serotype.
Conclusions: Invasive pneumococcal disease significantly decreased in children with sickle cell disease < or = 10 years of age after pneumococcal conjugate vaccine licensure. Pneumococcal conjugate vaccine was effective even when controlling for herd immunity. Extending guideline recommendations for catch-up vaccination beyond 4 years of age should be considered.