Social determinants of human papillomavirus vaccine series completion among U.S. adolescents: A mixed-methods study.

Introduction: Human papillomavirus (HPV) vaccination can significantly reduce HPV-associated cancers. In the US, two doses are recommended for vaccine completion for younger adolescents. However, series completion rates remain below the nation's goal of 80% coverage. Multi-faceted factors may influence adolescent series completion. The purpose of this study was to identify individual-level, relationship-level, and community-level factors of timely series completion among adolescents, ages 11-14, initiating the HPV vaccine series in 2017. Methods: A convergent, mixed-methods design was used combining adolescent electronic health record data (n = 803) and qualitative interviews with adolescents and their parents (n = 32) to assess timely series completion within 14-months (e.g., January 2018 to February 2019). Multivariable logistic regression analysis examined individual-level and community-level factors influencing timely series completion. Directed content analysis was used to identify relevant themes and subthemes. We provided an integrative summary to assess patterns of convergence or divergence between quantitative and qualitative data. Results: In the quantitative phase, 61.0% of adolescents completed the vaccine series and 47.3% completed it on-time. Higher odds of timely series completion were among younger adolescents at vaccine initiation (aOR = 1.82, 95%CI = 1.07, 3.11) and lower among adolescents who were Black (aOR = 0.57, 95%CI = 0.37, 0.89) and Hispanic (aOR = 0.54, 95%CI = 0.30, 0.95) compared to Non-Hispanic White adolescents and those without private insurance (aOR = 0.56, 95%CI = 0.37, 0.85). Qualitative findings revealed increased risk for HPV at sexual debut as a motivator for timely series completion. Family/peers and healthcare providers influenced timely series completion among minority adolescents. Community-level factors were not significantly associated with timely series completion, however, qualitative findings revealed lack of transportation as a barrier to timely series completion. Conclusion: Multi-level factors continue to influence timely series completion, despite fewer doses needed for series completion. Innovative strategies are needed to improve care coordination for receiving vaccine doses, patient-provider communication about series completion and increase access to HPV vaccine.