Abstract
Clinical trials remain the gold standard for evaluating the effectiveness and safety of health interventions. Every clinical trial is mandated to be registered prospectively in a publicly accessible trial registry before the enrollment of the first participant. The aim of the current study was to provide a cross-sectional analysis of registered HPV vaccine clinical trials listed in the International Clinical Trials Registry Platform (ICTRP). On 05 March 2023, we searched the ICTRP for registered HPV vaccine clinical trials using the term "human papillomavirus vaccine." Two authors independently extracted data including the name of the clinical trial registry, location, recruitment status, gender of participants, phase, primary outcome, and type of sponsor. Our search of the ICTRP resulted in 437 HPV vaccine clinical trials registered between 1999 and 2022. Most of the trials were: registered retrospectively (61.3%, n = 268), registered in ClinicalTrials.gov registry (66.8%, n = 292), conducted in Europe (26.0%, n = 112), not recruiting (80.5%, n = 352), in phase 3 (37.3%, n = 163), conducted among female participants (64.3%, n = 281), studying immune responses (46.7%, n = 204), and sponsored by pharmaceutical companies (50.3%, n = 220). To increase research transparency, prevent duplication of research, and prevent publication bias, there is an urgent need for all primary registries to make prospective registration mandatory and remain the only type of registration available to trial sponsors. All clinical trial primary registries should also make the completion of all fields compulsory when registering a trial to improve transparency.