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- gynaecological oncology
- quality in health care
- public health
- preventive medicine
- paediatric infectious disease & immunisation
The Cochrane Review conducted trial searches up until June 2017 and included 26 randomised trials with 73 428 women.1 In January 2018, we published an index of the study programmes of the HPV vaccines that included 206 comparative studies.2 As of June 2017, about a third of the 206 studies were not published and half of the completed studies listed on ClinicalTrials.gov had no results posted.2 Although we sent our index to the Cochrane group handling the Cochrane Review, the review stated that, ‘nearly all end-of-study reports have been published in the peer-reviewed literature’. When we applied the Cochrane Review’s inclusion criteria to the 206 studies, we identified 46 completed and eligible trials. The number of randomised participants could be assessed for 42 of the 46 trials and was 121 704. With nearly half of the trials and half of the participants missing, the Cochrane authors’ conclusion, ‘that the risk of reporting bias may be small’, was inappropriate. Fifteen of the 20 additional trials were listed on ClinicalTrials.gov; the Cochrane authors would therefore have identified more trials if they had searched ClinicalTrials.gov in more depth and searched additional trial registers (we searched 45 trial registers2).
The Cochrane authors stated that they ‘did not include the nine-valent vaccine [Gardasil 9] … since the randomised trials … did not incorporate an arm with a non-HPV vaccine control’. This is not correct. The only saline placebo trial of approved HPV vaccines is a Gardasil 9 trial (V503-006; NCT01047345) that was published in 2015.3 Its participants had previously been vaccinated with four-valent Gardasil, but according to the Cochrane Review protocol,4 this was not an exclusion criterion. Since many countries are shifting to Gardasil 9,5 it is unfortunate that the Gardasil 9 trial was not included in the Cochrane …
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