Presentation (CTI)

OBJECTIVES: Accurate assessment of vaccination coverage is essential for identifying low-coverage areas and targeting immunization activities. In Japan, where routine vaccination records are managed by individual municipalities, records for in-migrants from other municipalities may be incomplete. This study investigated how correcting incomplete municipal vaccination records for in-migrants changed the identification of low-coverage areas.
METHODS: We analyzed anonymized resident registry and vaccination data from one municipality in the VENUS Study database for FY2018-2022. The study sample consisted of residents aged 2-4 years at the end of FY2022. The analysis focused on pediatric pneumococcal conjugate vaccination because its multi-dose schedule may make coverage assessment sensitive to incomplete records. Vaccination completion rates for each small area within the municipality were calculated before and after correcting the completion status of in-migrants without vaccination records, based on the municipality-wide completion proportion among continuous residents. Low-coverage areas were defined as areas in the lowest quartile of completion rates. We quantified changes in low-coverage area classification using the number and proportion of reclassified areas and Cohen’s kappa.
RESULTS: The estimated overall completion rate increased from 89.4% to 98.3% after correction. Among 77 areas, 22 (28.6%) were reclassified into or out of the low-coverage group. Agreement between the classifications before and after correction was limited, with a Cohen’s kappa of 0.26. In a sensitivity analysis restricted to areas with at least 50 eligible residents, 20 of 61 areas (32.8%) were reclassified, with a Cohen’s kappa of 0.15.
CONCLUSIONS: Correcting incomplete vaccination records for in-migrants changed low-coverage area identification in more than one quarter of the areas analyzed, suggesting that municipal records alone may misidentify areas requiring targeted immunization activities. These findings highlight the importance of considering incomplete vaccination records for in-migrants when assessing area-level vaccination coverage and allocating limited resources.