(P-150) Differential Demographic and Clinical Characteristics Between MMR Vaccinated and Unvaccinated Children in South Korea

Background: Despite the high vaccination coverage of the combined measles-mumps-rubella (MMR) vaccine in South Korea, there still remains a risk of measles outbreak. In this context, substantial factors associated with MMR unvaccination need to be clarified.

Objectives: To identify differential demographic and clinical characteristics between MMR vaccinated and unvaccinated groups and explore vaccine utilization in MMR unvaccinated group.

Methods: We used a large-linked database to identify children aged 0 to 24 months born between 2008 and 2016 by combining data from the Korea Immunization Registry System and National Health Information database. MMR vaccination status was ascertained up to 24-month of birth to define MMR vaccinated and unvaccinated groups. We excluded children who died within 24-month of birth or received MMR vaccine out-of-schedule (1st dose of MMR vaccine beyond 24-month of birth). Socioeconomic status such as residence type, insurance type, and parental income level were assessed at the date of MMR vaccination, and comorbid conditions and healthcare utilizations were assessed 12-month period prior to date of MMR vaccination. To identify factors associated with MMR unvaccination, we conducted multivariate logistic regression to estimate odds ratios (ORs) with 95% confidence intervals (CIs). In addition, we assessed vaccination coverage of the routinely administered vaccines by the first year of birth, stratified by MMR vaccination status.

Results: Of 3,973,253 children included in our study, 3,897,579 (98.1%) received and 75,674 (1.9%) did not receive MMR vaccine. Compared with MMR vaccinated group, underutilization of healthcare resources was more notable in MMR unvaccinated group (number of outpatient visit [5.73±12.1 vs. 25.8±17.06]; days hospitalized [1.69±14.5 vs. 2.32±6.90]). Children were more likely not to receive MMR vaccine if they were born with congenital anomaly (OR 2.12; 95% CI 1.90-2.36), never admitted to intensive care unit (1.88; 1.78-1.98), or never visited emergency room (3.57; 3.53-3.72). Parental factors such as low income level (3.66; 3.58-3.74), local-subscriber health insurance (7.34; 7.21-7.46), or residing in metropolitan area (1.44; 1.41-1.46) were more likely to be observed in the MMR unvaccinated group. Moreover, vaccination coverage across 6 vaccines in this group remained below 50% throughout the study period.

Conclusions: There were substantial factors associated with MMR unvaccination and a notable underuse of the routinely recommended vaccines among MMR unvaccinated group, underscoring a need to implement targeted interventions in this subset of children in South Korea.