1. individuals vaccinated according to some alternative immunization schedules;
  2. variations in immunization schedules because of different immunization policies in the participating health plans, variations in clinical practice, vaccine shortages, problems with access, or parental decisions to delay vaccinations;
  3. multiple outcomes, including adverse events, diagnoses, and procedures as well as mortality;
  4. covariates, including race, age, gender, and zip code–level demographics; and
  5. global indices of shorter-term child health and service utilization, including numbers of days hospitalized, numbers of emergency room visits, and so forth.

Accordingly, secondary analyses of the data in VSD databases would add to current knowledge and help answer the four primary research questions listed in Box 6-1. For example, in a review of alternative immunization schedules in the Kaiser Permanente Colorado system, VSD researchers initiated a retrospective matched cohort study to examine patterns and trends for children defined as undervaccinated at ages 2 to 24 months and compared the health care utilization rates between undervaccinated children and children vaccinated at the appropriate age.

Eight sites in the VSD participated in this study. Of 323,247 children born (within the participating managed care organization sites) between 2004 and 2008, 48.71 percent were considered undervaccinated for at least 1 day before age 24 months. The prevalence and specific patterns of undervaccination significantly increased across the study duration. In a matched cohort analysis, undervaccinated children had a significantly lower outpatient visit rate (11 percent) than did children who were vaccinated in an age-appropriate manner. In contrast, undervaccinated children had significantly greater (25 percent more) inpatient hospital admission rates than did children vaccinated at the appropriate age.

In a second matched cohort analysis, children who were undervaccinated because of parental choice had fewer outpatient visits and emergency room encounters than did children vaccinated at the appropriate age. In this second matched cohort analysis, no significant detectable difference in inpatient visit rates was detected between the two groups. Among children considered undervaccinated for any reason, 1,399 instances of undervaccination (variations in immunization history that could indicate alternative schedules) were detected. Among children undervaccinated because of parental choice, 756 distinct instances of undervaccination were detected (Glanz et al., 2013). More study will clearly be needed to draw conclusions

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