Quality Improvement to Immunization Coverage in Primary Care Measured in Medical Record and Population-Based Registry Data

Published:February 03, 2018DOI:



      Despite the proven benefits of immunizations, coverage remains low in many states, including Vermont. This study measured the impact of a quality improvement (QI) project on immunization coverage in childhood, school-age, and adolescent groups.


      In 2013, a total of 20 primary care practices completed a 7-month QI project aimed to increase immunization coverage among early childhood (29–33 months), school-age (6 years), and adolescent (13 years) age groups. For this study, we examined random cross-sectional medical record reviews from 12 of the 20 practices within each age group in 2012, 2013, and 2014 to measure improvement in immunization coverage over time using chi-squared tests. We repeated these analyses on population-level data from Vermont's immunization registry for the 12 practices in each age group each year. We used difference-in-differences regressions in the immunization registry data to compare improvements over time between the 12 practices and those not participating in QI.


      Immunization coverage increased over 3 years for all ages and all immunization series (P ≤ .009) except one, as measured by medical record review. Registry results aligned partially with medical record review with increases in early childhood and adolescent series over time (P ≤ .012). Notably, the adolescent immunization series completion, including human papillomavirus, increased more than in the comparison practices (P = .037).


      Medical record review indicated that QI efforts led to increases in immunization coverage in pediatric primary care. Results were partially validated in the immunization registry particularly among early childhood and adolescent groups, with a population-level impact of the intervention among adolescents.


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