Purpose of study: Health departments (HDs) are at the forefront of efforts to improve HPV vaccine uptake in the US. Most notably, HD staff routinely conduct in-person quality improvement (QI) coaching to help primary care clinics improve their vaccine delivery systems. Some HDs also engage outside experts to conduct remote physician communication training to help vaccine prescribers recommend HPV vaccine more effectively. To guide future HD programming, we sought to understand the implementation strengths and challenges of QI coaching and physician communication training. Methods: In a cluster randomized trial, we allocated 855 primary care clinics in 3 geographically-diverse US states to receive: 1) QI coaching; 2) physician communication training; or 3) both interventions combined. In each arm, we assessed adoption (or the % of clinics receiving the allocated intervention out of those invited), contacts per clinic (mean number of contacts needed to successfully schedule one clinic), reach (median number of total staff and prescriber participants per clinic), and delivery cost. Results: More clinics adopted QI coaching than communication training or the combined intervention (63% vs 16% and 12%, both p<.05). Recruiting clinics into QI coaching sessions required fewer contacts than communication training or the combined intervention (mean = 4.7 vs 29.0 and 40.4, both p<.05). In contrast, communication training and the combined intervention reached more total staff per clinic than QI coaching (median = 5 and 5 vs 2, both p<.05), including more prescribers per clinic (2 and 2 vs 0, both p<.05). QI coaching cost $439 per clinic on average, including costs incurred from follow up ($129/clinic), session preparation ($73/clinic), and travel ($69/clinic). Communication training cost $1,287 per clinic, with most cost incurred from clinic recruitment ($653/clinic). Conclusions: QI coaching was lower cost and had higher adoption, but remote communication training achieved higher reach, including to highly influential vaccine prescribers. Thus, communication training is a promising intervention for improving HPV vaccine delivery, although care will be needed to overcome substantial challenges to clinic recruitment.