Completion of human papillomavirus vaccination and its determinants among adolescents in Southern Ethiopia: a convergent parallel mixed-methods study

Background: Cervical cancer is the second most common cancer among women in Ethiopia and is primarily attributable to human papillomavirus (HPV) infection. Although HPV vaccination has been introduced, completion of the recommended two-dose schedule remains suboptimal. Existing evidence has largely focused on access and awareness, with limited attention to cognitive, sociocultural, and maternal decision-making factors influencing completion. This study assessed the magnitude and determinants of second-dose or complete HPV vaccination among adolescents in southern Ethiopia using a mixed-methods approach. Methods: A community-based cross-sectional survey was conducted among 832 mothers of adolescent girls aged 9-14 years, selected using a multistage sampling method. Data were collected using a semi-structured questionnaire and analyzed with IBM SPSS ver. 23.0. A binary logistic regression model was used to identify factors associated with vaccine completion. Additionally, in-depth interviews were conducted with 12 purposively selected mothers and analyzed thematically to explore perceptions influencing vaccine completion. Results: The proportion of adolescents who completed the HPV vaccination series was 26.3% (95% confidence interval, 23.3-29.3). Factors positively associated with complete vaccination included maternal education at the secondary or higher, shared or autonomous maternal decision-making, prior cervical cancer screening and good knowledge of HPV. Conversely, high information overload and decision fatigue were associated with lower odds of completing the vaccination schedule. Qualitative findings revealed that mothers' decisions were shaped by cultural beliefs, trust in health workers, peer and social media influences, and prior healthcare experience. Conclusion: HPV vaccination completion was low and was associated with interacting cognitive, socio-cultural, and health-system factors. Interventions should move beyond awareness creation to address information burden, strengthen maternal decision-making autonomy, and improve trust through consistent counseling.