<p><strong>PURPOSE: </strong>The purpose of this study was to describe patterns of human papillomavirus (HPV) vaccine initiation by males and characterize sociodemographic differences.</p>

<p><strong>METHODS: </strong>We conducted a retrospective cohort study of 11- to 18-year-old males in a large primary care network who had a preventive or acute visit between October 2009 and December 2013. Outcomes measured were HPV vaccine series initiation and initiation at the first eligible visit. Logistic regression measured independent associations between outcomes and sociodemographic characteristics, adjusting for potential confounders including visit frequency, insurance changes, and the presence of complex medical conditions.</p>

<p><strong>RESULTS: </strong>Of 58,757 eligible patients, most were white (57%) with private insurance (77%). During the study period, 39% of the cohort initiated the vaccine series, and 7% initiated at their first eligible visit. Black patients with private (adjusted odds ratio [aOR], 1.99; 95% confidence interval [CI], 1.73-2.30) and Medicaid insurance (aOR, 2.90; 95% CI, 2.56-3.30) had significantly higher odds of HPV vaccine initiation compared with white patients with private insurance. A similar trend was found for Hispanic patients with private (aOR, 1.45; 95% CI, 1.26-1.67) and Medicaid insurance (aOR, 2.15; 95% CI, 1.78-2.60). These differences were present both in the preroutine recommendation period (2009-2011) and the postroutine recommendation period (2012-2013).</p>

<p><strong>CONCLUSIONS: </strong>Traditionally marginalized populations have higher odds of HPV vaccine initiation, both at the first eligible visit and overall. Although the true mechanism underlying these differences remains unknown, potential candidates include provider recommendation patterns and differential vaccine acceptance within these groups.</p>