Uptake of pneumococcal conjugate vaccine among children in the 1998-2002 United States birth cohorts

Background: Routine childhood immunization with pneumococcal conjugate vaccines (PCV7s) began in 2000 in the United States. Despite vaccine shortages, reductions in invasive pneumococcal disease occurred rapidly during 2000-2002. Age-appropriate PCV7 coverage was estimated and characteristics associated with undervaccination were identified for children in the 1998-2002 birth cohorts. Methods: Data were analyzed for 85,135 children aged 19-35 months in the 2001-2004 National Immunization Surveys. To obtain PCV7 coverage estimates by birth cohorts, a pooled analysis was conducted by combining individual survey years that sampled children with appropriate birth dates. Logistic regression models were used to identify factors associated with age-appropriate vaccination. Results: The proportion of children receiving the primary 3-dose PCV7 series by age 12 months increased from 45.5% (+/- 0.6) among children born in 2000 to 62.1% (+/- 0.7) among those born in 2002. By age 24 months, an estimated 30.7% (+/- 0.6), 38.0% (+/- 0.6), and 49.0% +/- 1.1) of children born in 2000, 2001 and 2002, respectively, had received all four PCV7 doses; however, only 15.0% (+/- 0.4), 16.1% (+/- 0.4) and 24.4% (+/- 0.6) of children were age-appropriately immunized. Among children born in 1998 and 1999, 10.1% +/- 0.5) and 37.6% (+/--0.7), respectively, received one or more catch-up doses during their second year of life. Lower age-appropriate PCV7 coverage was independently associated with black race, Hispanic ethnicity, receiving vaccinations from public health providers, and low household income. Conclusions: The dramatic reductions in pneumococcal-related diseases from direct and indirect vaccine effects occurred when few children had received the recommended complete vaccine schedule, and there were substantial racial and socioeconomic disparities in coverage.