Magnitude and factors associated with missed Human Papillomavirus vaccination opportunities among adolescents in Dar es Salaam, Tanzania

Background: Tanzania introduced the human papillomavirus (HPV) vaccine in 2018 for girls aged 9-14 years; however, coverage remains suboptimal. Missed opportunities (MOs) for vaccination are an important but understudied barrier, particularly in urban settings. This study assessed factors associated with MOs and explored healthcare providers perspectives on barriers and potential solutions in Dar es Salaam. Methods: An embedded mixed-methods study was conducted in public health facilities in Temeke Municipal Council from June - July 2025. The quantitative component involved a cross-sectional survey of 252 parents or caregivers of eligible adolescent girls using structured exit interviews. The qualitative component included in-depth interviews with 20 healthcare providers using a phenomenological approach. Multivariable logistic regression identified factors associated with MOs. Qualitative data were analyzed thematically using Braun and Clarkes framework. Results: The prevalence of MOs for HPV vaccination was 71.4%. Factors independently associated with MOs included caregiver age [≥]40 years (aOR 1.87, 95% CI: 1.02-3.42), female caregiver gender (aOR 1.61, 95% CI: 1.00-2.59), primary education (aOR 2.14, 95% CI: 1.03-4.45), married status (aOR 1.72, 95% CI: 1.01-2.94), and receiving care at health centers or dispensaries versus hospitals (aOR 1.83, 95% CI: 1.05-3.19). Qualitative findings identified key drivers of MOs, including limited caregiver knowledge, vaccine hesitancy, time constraints, failure to routinely offer vaccination, stock-outs, poor documentation, high workload, and limited outreach. Proposed strategies included routine eligibility screening, reminder systems, community engagement, and supportive supervision. Conclusion: MOs for HPV vaccination are highly prevalent and driven by both caregiver and health system factors. Strengthening routine screening, reminder systems, community engagement, and supervision may improve vaccine uptake.