Vaccination Coverage Levels Among Young Children in the Vaccine Safety Datalink

Background: Routine assessment of childhood immunization levels in the United States is important to detect possible delays or drops in coverage. We estimated the vaccination coverage of children enrolled in the Vaccine Safety Datalink (VSD), a collaborative project between eight HMOs that captures data on more than 9.5 million people (2.3 million children) annually.

Objectives: To (1) assess vaccination coverage levels in VSD-enrolled children aged 19, 24, and 35 months during 2005, 2006 and 2007, and (2) compare VSD coverage levels to corresponding National Immunization Survey estimates.

Methods: Coverage was examined over three years to evaluate consistency in coverage levels, detect possible trends, and evaluate any effect of vaccine shortages. Data were included for children who were enrolled for at least one year immediately prior to age of interest and who had at least one well-child visit during that enrollment period.

Results: The percentage of VSD participants aged 19, 24, and 35 months who were up to date with the 4:3:1:3, 4:3:1:3:3 and 4:3:1:3:3:1 vaccination series decreased from 2005 to 2007. Coverage with the 4:3:1:3:3:1 series was 89.7% (+/- 0.2) among 35 month olds in 2005, but decreased to 88.5% (+/- 0.2) in 2006 and 85.3% (+/- 0.3) in 2007. Coverage with at least four doses of pneumococcal conjugate vaccine, the newest vaccine examined, increased annually, from 69.8% (+/- 0.3) of 19 month olds in 2005 to 86.2% (+/-0.3) in 2006 and 87.1% (+/- 0.3) in 2007. VSD coverage estimates in each age group were consistently higher than NIS estimates; VSD estimates for the three routine vaccination series ranged from 5% to 7% higher than NIS estimates among 24 month olds in 2007.

Conclusions: Coverage with routine childhood vaccination series decreased slightly over the three year study period. As expected, vaccine coverage among children in an insured population was higher than national estimates.