Index of the human papillomavirus (HPV) vaccine industry clinical study programmes and non-industry funded studies: a necessary basis to address reporting bias in a systematic review

Background: Unabridged access to drug industry and regulatory trial registers and data reduces reporting bias in systematic reviews and may provide a complete index of a drug's clinical study programme. Currently, there is no public index of the human papillomavirus (HPV) vaccine industry study programmes or a public index of non-industry funded studies.

Methods: By cross-verification via study programme enquiries to the HPV vaccine manufacturers and regulators and searches of trial registers and journal publication databases, we indexed clinical HPV vaccine studies as a basis to address reporting bias in a systematic review of clinical study reports.

Results: We indexed 206 clinical studies: 145 industry and 61 non-industry funded studies. One of the four HPV vaccine manufacturers (GlaxoSmithKline) provided information on its study programme. Most studies were cross-verified from two or more sources (160/206, 78%) and listed on regulatory or industry trial registers or journal publication databases (195/206, 95%)-in particular, on ClinicalTrials.gov (176/195, 90%). However, study results were only posted for about half of the completed studies on ClinicalTrials.gov (71/147, 48%). Two thirds of the industry studies had a study programme ID, manufacturer specific ID, and national clinical trial (NCT) ID (91/145, 63%). Journal publications were available in journal publication databases (the Cochrane Collaboration's Central Register of Controlled Trials, Google Scholar and PubMed) for two thirds of the completed studies (92/149, 62%).

Conclusion: We believe we came close to indexing complete HPV vaccine study programmes, but only one of the four manufacturers provided information for our index and a fifth of the index could not be cross-verified. However, we indexed larger study programmes than those listed by major regulators (i.e., the EMA and FDA that based their HPV vaccine approvals on only half of the available trials). To reduce reporting bias in systematic reviews, we advocate the registration and publication of all studies and data in the public domain.