Presentation (CTI)

OBJECTIVES: We aimed to measure the HPV vaccine completion rate among Kentucky Medicaid beneficiaries who had already received their first dose and identify key factors influencing vaccine series completion.
METHODS: We conducted a retrospective cohort study to evaluate the HPV vaccine completion rate using Medicaid claims data from Kentucky, covering 2010 to 2022. To capture a 12-month follow-up and a look-back period around the index date (defined as the first vaccine dose), the study included beneficiaries with at least one vaccine claim during 2011 to 2021. We then used an extreme gradient boosting (XGBoost) with the SHAP approach to identify the nonlinear effects of covariates on HPV vaccine series completion. The covariates included race, ethnicity, sex, age group, rurality score, provider type, and managed care organization (MCO) type.
RESULTS: Approximately 37% of the 166,063 continuously enrolled, vaccine-naïve individuals completed two or more doses of the HPV vaccine. We found the highest rates of vaccine completion among those aged 9-10 (60.5%), White (38.8%), patients visiting individual physician providers (53%), and living in a rural code of 7 (42%). Males and females contributed approximately equally to completion rates. Our XGBoost model (overall accuracy: 66.4%) identified age 11-12, coverage by an MCO, and a physician individual provider as the primary drivers of completion. Regarding interaction effects, initiation at ages 9-12 was associated with a higher chance of completion among females. Additionally, those living in urban areas who initiated at 9-10 were more likely to complete the series.
CONCLUSIONS: The HPV vaccine was completed mainly by the youngest age groups, those who used an MCO, and those who visited a physician or individual provider. Among the early initiators, males and rural residents had a lower likelihood of completing the vaccine series, which warrants greater attention to healthcare access for these groups.