Non-publication and delayed publication of randomized trials on vaccines: a survey

Objective To evaluate the extent of non-publication or delayed publication of registered randomized trials on vaccines, and to investigate potential determinants of publication delay. Design Survey. Data sources Trials registry websites, Scopus, PubMed, Google. Study selection and Methods We included randomized trials (RCTs) evaluating the safety and/or efficacy/immunogenicity of papillomavirus (HPV), 2009 H1N1 influenza, meningococcal, pneumococcal and rotavirus vaccines, that were registered in ClinicalTrials.gov, ISRCTN, WHO ICTRP, Clinical Study Register, or Indian, Australian New Zealand, and Chinese trial registries in 2006-2012. We searched electronic databases up to February 2014 to identify published manuscripts containing trial results, which were reviewed and classified as positive, mixed or negative. The results available into ClinicalTrials.gov were also reviewed. Main outcome measures Publication status of trial results, time from completion to publication into peer reviewed journals. Data synthesis: Potential predictors of publication delay were evaluated using Cox proportional hazards regression. Results We analysed 384 trials (84.9% industry-sponsored). 355 trials (n = 404,758 participants) had been completed, and, of those, 176 trials (n = 151,379) had been published into peer-reviewed journals. Another 42 trials (total sample = 62,765) remained unpublished but reported results in ClinicalTrials.gov. The proportion of trials published 12, 24, 36, and 48 months after completion was 11.9%, 28.8%, 53.1% and 73.0%. Including results posted in ClinicalTrials.gov, 48 months after study completion results were available for 82.4% of the trials and 89.6% of the participants. No difference in the publication delay was observed between non-industry and industry sponsored trials, but the former were 4.42-fold (p = 0.008) more likely to report negative/mixed findings. Negative results were reported only by 2.3% of the published trials. Conclusions The majority of vaccine trials either get published eventually or have results posted in ClinicalTrials.gov, but delays of several years in their publication are very common. Actions should focus on the timely public dissemination of vaccine trial data. Key messages As compared to other fields of Medicine, our estimate that results on approximately 80% of the participants to vaccine trials can be published in journals 4 y after trial completion is quite favourable. No differences were found in the publication delay between non-industry and industry sponsored trials, but the former were more likely to report negative findings.