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Assessing misclassification of vaccination status: Implications for studies of the safety of the childhood
Matthew F Daley1, Jason M Glanz2, Sophia R Newcomer2
1Institute for Health Research, Kaiser Permanente Colorado, Denver, CO, United States; Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO, United States.
Insights
Electronic health records can accurately identify children with delayed vaccinations due to parental choice, minimizing misclassification risks in vaccine safety studies. This improves the reliability of comparing health outcomes between vaccinated and under-vaccinated children.
Area of Science:
- Pediatric Health
- Vaccine Safety Research
- Health Informatics
Background:
- Public concern exists regarding the safety of childhood immunization schedules.
- Observational studies are recommended to compare adverse health outcomes between fully vaccinated and under-vaccinated children.
- Accurate classification of vaccination status is crucial to prevent bias in these studies.
Purpose of the Study:
- To assess the risk of misclassification of vaccination status within the Vaccine Safety Datalink (VSD).
- To evaluate the accuracy of electronic health record (EHR) data in identifying under-vaccinated children due to parental choice.
Main Methods:
- A retrospective cohort study utilizing EHR data and parent surveys.
- Phase 1: Identified patterns of under-vaccination in the first 24 months of life.
- Phase 2 & 3: Manual review of records and parent surveys to confirm vaccination status and reasons for under-vaccination.
Main Results:
- The study analyzed 361,901 children born between 2004 and 2012.
- Electronic health record data, combined with diagnosis codes for vaccine refusal, accurately identified nearly 100% of under-vaccinated children due to parental choice.
- Parent surveys confirmed EHR findings and indicated under-vaccinated children's parents were more likely to use alternative providers.
Conclusions:
- Electronic health records and diagnosis codes can reliably identify specific groups of under-vaccinated children.
- This method minimizes the risk of misclassification bias in vaccine safety studies.
- The findings support the use of EHR data for vaccine safety research involving parental vaccine choice.
Background:
To 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.
Objective:
To assess risk of misclassification of vaccination status within the Vaccine Safety Datalink (VSD).
Design/Methods:
A 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 24months 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.
Results:
The study cohort included 361,901 children born 2004 through 2012. By 24months of age, 198,249 (54.8%) were fully vaccinated with no delays, 84,698 (23.4%) experienced delays but were fully vaccinated by 24months of age, 4865 (1.3%) received no vaccines, 3789 (1.0%) delayed starting vaccination until ≥4months 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.
Conclusions:
Specific 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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