Assessing misclassification of vaccination status: Implications for studies of the safety of the childhood immunization schedule |
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| Institution: | 1. Institute for Health Research, Kaiser Permanente Colorado, Denver, CO, United States;2. Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO, United States;3. Group Health Research Institute, Seattle, WA, United States;4. Kaiser Permanente Northwest, Portland, OR, United States;5. Kaiser Permanente Southern California, Pasadena, CA, United States;6. Marshfield Clinic Research Foundation, Marshfield, WI, United States;7. Kaiser Permanente Northern California, Oakland, CA, United States;8. Immunization Safety Office, Division of Healthcare Quality Promotion, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA, United States;1. Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC;2. Duke Cancer Institute, Duke University Medical Center, Durham, NC;1. Centre for the Evaluation of Vaccination, Vaccine & Infectious Disease Institute, Faculty of Medicine and Health Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Antwerp, Belgium;2. Flemish Agency for Care and Health, Infectious Disease Control and Vaccinations, Belgium;3. Department of Public Health and Primary Care, Centre for Youth Health Care, KU Leuven, Belgium;4. Fund of Scientific Research (FWO), Belgium;1. Department of Obstetrics, Gynecology and Reproductive Sciences, Larner College of Medicine, University of Vermont, Burlington, VT, United States;2. Department of Medical Biostatistics, Larner College of Medicine, University of Vermont, Burlington, VT, United States;1. Department of Urologic Oncology, School of Medicine, University of Colorado Denver, Aurora, Colorado;2. Division of Medical Oncology, Department of Medicine and Department of Urology, School of Medicine, University of Washington and Fred Hutchinson Cancer Research Center, Seattle, Washington;3. Carolina Urologic Research Center, Myrtle Beach, South Carolina;4. University of Michigan Comprehensive Cancer Center, Ann Arbor, Michigan;5. Smilow Cancer Center, Yale University, New Haven, Connecticut;1. Veterans Aging Cohort Study Coordinating Center, VA Connecticut Healthcare System, West Haven, CT, USA;2. Internal Medicine, Yale University School of Medicine, New Haven, CT, USA;3. Epidemiology & Population Health, London School of Hygiene & Tropical Medicine, London, UK;4. Division of Infectious Diseases, Atlanta VA Medical Center, Decatur, GA, USA;5. School of Medicine, Emory University, Atlanta, GA, USA;6. Rollins School of Public Health, Emory University, Atlanta, GA, USA;7. Medicine, James J. Peters VA Medical Center, New York, NY, USA;8. Icahn School of Medicine, Mount Sinai, New York, NY, USA;9. Medicine, Michael E. DeBakey VA Medical Center, Houston, TX, USA;10. Medicine-Infectious Diseases, Baylor College of Medicine, Houston, TX, USA;11. Medicine, VA Greater Los Angeles Healthcare System, Los Angeles, CA, USA;12. David Geffen School of Medicine, UCLA, CA, USA;13. Medicine, Washington DC VA Medical Center, Washington, DC, USA;14. Medicine (Division of Infectious Diseases) and Department of Epidemiology, Biostatistics, and Informatics, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, USA;15. School of Public Health, Yale University, New Haven, CT, USA;p. Center for Interdisciplinary Research on AIDS, Yale University, New Haven, CT, USA |
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| Abstract: | BackgroundTo address public concern about the safety of the childhood immunization schedule, the Institute of Medicine recommended observational studies comparing adverse health outcomes of fully vaccinated children to children under-vaccinated due to parental choice. Misclassification of vaccination status could bias such studies.ObjectiveTo assess risk of misclassification of vaccination status within the Vaccine Safety Datalink (VSD).Design/methodsA retrospective cohort study was conducted in three phases. In phase 1, electronic health record (EHR) data were used to identify patterns of under-vaccination during the first 24 months of life potentially due to parental choice. In phase 2, a random sample of records of under-vaccinated children was manually reviewed. In phase 3, a separate sample of parents were surveyed to assess whether EHR data accurately reflected their child’s vaccination status. Phases 1 and 2 were conducted at 6 VSD sites, phase 3 at 1 site.ResultsThe study cohort included 361,901 children born 2004 through 2012. By 24 months of age, 198,249 (54.8%) were fully vaccinated with no delays, 84,698 (23.4%) experienced delays but were fully vaccinated by 24 months of age, 4865 (1.3%) received no vaccines, 3789 (1.0%) delayed starting vaccination until ≥4 months of age, 4781 (1.3%) had consistent vaccine-limiting (≤2 vaccines per visit), and the remaining 65,519 (18.1%) were missing vaccine series or doses. When a diagnosis code for vaccine refusal was present in EHR data, encounter notes confirmed vaccine refusal as the reason for under-vaccination for nearly 100% of sampled records. Parent surveys confirmed these findings. Parents of under-vaccinated children were more likely to report visiting an alternative medical provider than parents of fully vaccinated children.ConclusionsSpecific groups of children, under-vaccinated due to parental choice, can be identified with relatively low likelihood of misclassification of vaccination status using EHR-based vaccine data and diagnosis codes. |
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| Keywords: | Vaccine safety Vaccine schedule Vaccine Immunization Under-vaccination Child |
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