Clear and complete reporting of studies about the effects of vaccination are important for readers to be able to locate relevant studies, understand their findings and assess their validity. Vaccination is one of the most effective interventions known to prevent childhood mortality and morbidity from infectious diseases,1 and randomized controlled trials (RCTs) are needed to obtain licensure and guide decisions about their use. RCTs are considered to be the gold standard for the evaluation of healthcare interventions because, when well designed and conducted, they are at lower risk of bias and confounding than other study designs.2,3 However, empirical studies of published trials have shown that RCT results can be biased through processes such as inadequate randomization processes and exclusion of participants after randomization (Table 1).4–11 Additionally, trials that have been well conducted but incompletely reported could be falsely judged as being at risk of bias. The completeness of reporting is becoming more important as health agencies, including the World Health Organization, now use formalized processes such as Grades of Recommendation Assessment, Development and Evaluation to assess the strength of evidence, based on descriptions of trial features, when making vaccine-related policy decisions.28–30
Reporting guidelines are statements that give advice to authors on how to report the key features of research methods and findings so that readers have a clear and transparent account of what was done and what was found.31 The CONsolidated Standards Of Reporting of Trials (CONSORT) statement, which was developed to improve the reporting of RCTs, was the first reporting guideline to be widely published and adopted. The statement was first published in 1996 and updated in 2001 and 2010 and now consists of a 25-item checklist of reporting items, a flow chart and an elaboration document that explains each item and gives examples of good reporting.2,14,32 In the field of vaccination, there are already specific guidelines for reporting of safety data in vaccine trials produced by the Brighton Collaboration, a global network that conducts and promotes vaccine safety research.33,34
The completeness of reporting of RCTs has been examined in various areas of medical research, and studies show that key items are often not optimally reported.35–38 The completeness of reporting of vaccine safety39 and of factors specific to vaccine administration have been examined,40 but other methodological aspects of study design of vaccines have not, to our knowledge, been assessed. We conducted this study to describe the completeness of reporting of important methodological features of RCTs of vaccines.
MATERIALS AND METHODS
We followed a study protocol that was finalized before the start of the study (Supplemental Digital Content 1, https://links.lww.com/INF/B334). Amendments made after the study began are stated in the protocol.
We examined RCTs included in a convenience sample of 3 published systematic reviews of pneumococcal and rotavirus vaccines.13,26,41 Systematic reviews were used as the source of RCTs because extensive database searches to identify and select relevant publications had already been conducted. The selected reviews covered a range of vaccines and target age groups, including data on both childhood (pneumococcal conjugate and rotavirus) and adult (pneumococcal polysaccharide) vaccines, long-standing (pneumococcal polysaccharide vaccines [PPVs]) and recently developed (pneumococcal conjugate vaccines [PCVs] and rotavirus) vaccines and polysaccharide (PPV), conjugate (PCV) and live (rotavirus) vaccines. The search strategies for the reviews are reported in the original publications13,26,41 and the dates of the most recent searches were: May 10, 2007 for PPV; March 17, 2010 for PCV; and February 2, 2010 for rotavirus vaccine. The PCV review has been published in part and the reference list of RCTs for the full review is available from the authors on request. We examined trial registration documents and searched the PubMed database up to November 1, 2011 for subsequent publications of trials that were identified in 1 of the reviews but did not have a journal publication listed.
For each trial, we included the earliest publication that reported clinical efficacy, carriage or immunological outcomes. If it was unclear which publication was earliest, we included the publication that was submitted to a journal first. If this was not reported, we included the publication with the most detailed description of the methods. Some publications contained details of more than 1 potentially eligible trial. To avoid overrepresentation of an individual publication, only the first potentially eligible trial reported in each publication was included. In addition, we examined articles that were cited in the included publications as detailed descriptions of the trial methods but these were not counted in the numbers of included articles. We excluded abstracts and all reports that had not been published in a journal. Two independent reviewers applied the eligibility criteria to the publications included in each systematic review.
We developed a data collection form and data collection guide with 27 items about reporting, based on items in the CONSORT 2010 checklist and issues specific to RCTs of vaccines. In the main text, we report on the 13 items related to: identifying vaccine trial publications; assessing the potential for bias in individual trials; assessing potential harms of vaccination; and assessing age at vaccination (Table 1). The remaining 14 items are reported in the Table, Supplemental Digital Content 2, https://links.lww.com/INF/B335. Seven of the items reported in the main text were predefined as primary outcomes in the protocol because we had previously observed that these were often not reported:13,26 CONSORT item numbers 1a (identification in the title as a randomized trial), 6a (primary outcome defined), 8 (sequence generation reported), 9 (allocation concealment described) and 23 (trial registration number reported); intended age at vaccination reported; and actual ages at vaccination reported. The other 6 CONSORT items are: 11a (who is blinded reported), 13 (flow diagram presented), 13a (numbers receiving allocated treatment reported), 16 (denominator reported for primary outcome analysis), 16 (intention-to-treat analysis stated) and 19 (statement made about serious adverse events).
We looked for information about the use of the CONSORT statement for each journal that published at least 1 included RCT. First, we recorded from the CONSORT website whether the journal endorsed the statement. We then read the instructions to authors on the journal website and recorded whether there was an explicit statement about CONSORT. We recorded whether the journal asked authors to submit a CONSORT flow diagram, a checklist or both with their article.
Two reviewers (PS, FO) extracted and entered data independently from each publication. Discrepancies in data extraction were resolved by consensus. If there was no agreement, a third independent reviewer (NL) adjudicated to make a final decision.
We calculated the percentage of articles reporting each item for all trials and the exact confidence intervals. We then calculated these percentages separately for trials published in 2001 or before and 2002 or after to assess completeness of reporting after the influential first revision of the CONSORT statement.42 We examined each item separately for each journal with more than 5 included publications and also examined items separately for RCTs with more than and fewer than 1000 participants. Finally, we calculated the percentage of trials that reported a trial registration number each year. We did not perform any statistical hypothesis tests because power to detect differences was limited by the number of included trials.
Included Trials and Journals
We included 70 trials reported in 70 publications identified from systematic reviews of PPV, PCV and rotavirus vaccines (Fig. 1 and Supplemental Digital Content 3, https://links.lww.com/INF/B336). Of the total 88 RCTs included in the 3 reviews, we excluded 18; 12 for which we could find no journal publications and 6 that were not the first eligible RCT in publications that reported on multiple RCTs.
Of the included publications, 16 were about PPV, 27 about PCV and 27 about rotavirus vaccine (Fig. 1, Table 2). Forty-nine (70%) were published in the last decade (2002–2011). Almost all (69/70, 98%) were individually randomized or quasi-RCTs, and 42 of 70 (60%) were conducted in Europe or North America.
The 70 publications were published in 19 journals (Table 3). The journals with the most included publications were: The Pediatric Infectious Disease Journal (Pediatr Infect Dis J, 17 publications); Vaccine (16); The Lancet (8); and The New England Journal of Medicine (New Engl J Med, 6). The percentage of trials with >1000 participants was higher in The Lancet (5/8, 63%) and New Engl J Med (6/6, 100%) than Pediatr Infect Dis J (3/17, 18%) or Vaccine (3/16, 19%). The Lancet was the only 1 of these 4 journals that is both listed as endorsing the CONSORT and requires adherence to CONSORT in its instructions for authors. Of the 19 journals, 11 were listed on the CONSORT website in November 2011 as endorsing the CONSORT statement, but 2 of these did not mention CONSORT in their own instructions for authors (Journal of Pediatrics and New Engl J Med). Among the 11 journals endorsing CONSORT, 2 requested the submission of both the checklist and flow diagram, 1 the checklist only, 2 the flow diagram only and 4 asked authors to conform to CONSORT guidelines but did not ask specifically for the checklist or flow diagram. Of the 8 journals that were not listed on the CONSORT website, 2 mentioned CONSORT in the guide for authors and requested the submission of a flow diagram.
Reporting of CONSORT Items
Of the total of 70 publications, 14 (20%) identified the study as a randomized trial in the title (Table 4). This item was included in 7 of the 8 publications (88%) in The Lancet but in <15% of publications in New Engl J Med (0/6, 0%), Pediatr Infect Dis J (2/17, 12%) and Vaccine (1/16, 6%; Table 5). One or more primary outcomes were nominated in 26 publications (37%). A further 32 publications (46%) made reference only to a primary hypothesis or primary aim.
The method used to generate the random allocation sequence was fully reported in 24 publications (34%). The method of allocation concealment was completely reported in 9 publications (13%). A further 23 (33%) reported details that were insufficient to fully assess the adequacy of concealment. No information was given for 30 trials (61%) published in 2002 or after. Of trials published in the 4 most frequent journals, at least half of those in New Engl J Med (3/6, 50%), Pediatr Infect Dis J (10/17, 59%) and Vaccine (10/16, 62%) did not give any information regarding allocation concealment, whereas 7 of 8 published in The Lancet gave complete or partial information (Table 5).
Five publications (7%) made explicit statements about the blinding of participants, those administering the vaccine, those assessing clinical outcomes and laboratory workers (Table 4). A further 33 publications (47%) made explicit statements about the blinding of some, but not all, of these groups. Twenty-two publications (31%) used general terms such as “open” or “double-blind” without explicitly stating who was or was not blinded.
A flow diagram was presented in 30 publications (43%) overall and 26 (53%) in the last decade. Flow diagrams were published in half or less than half of trials published in the New Engl J Med (3/6, 50%), Vaccine (7/17, 41%) and Pediatr Infect Dis J (7/16, 44%) compared with 7 of 8 (88%) in The Lancet. The number of participants who received the allocated number of doses of vaccine were reported fully in 35 publications (50%). A further 7 publications (10%) reported the numbers either for all groups combined or for some but not all intervention groups. Twenty-eight publications (40%) did not report this item. The number of individuals included in primary outcome analyses was well reported in 20 (77%) of 26 publications that nominated a primary outcome.
The term “intention to treat” was used in relation to analyses in 22 publications (31%). The definition of intention to treat varied between publications, and some definitions suggested that randomized individuals would be excluded from analysis. Another 2 publications used the term “modified intention to treat,” which referred to analysis schemes where randomized individuals were excluded.
A statement about vaccine safety using the term “serious adverse events” was made in half the publications (36/70, 51%). Before 2002, only 14% (3/21) used this term and 67% (33/49) in 2002 and after. Publications in the last decade that mentioned safety but without the term “serious adverse events” made statements such as “In general, the vaccinations were well tolerated, and no immediate or severe adverse events were recorded” and “no participant was withdrawn due to a reaction to any of the vaccines.”
Trial registration numbers were first reported in included publications in 2006. Since then, the proportion of publications reporting a trial registration number has increased, and all publications in 2010 (6 publications) and 2011 (4 publications) had a trial registration number (Fig. 2). For CONSORT items, other than serious adverse events and trial registration numbers, there were no marked differences between trials published before and after 2002.
The CONSORT items shown in Table 4 were generally reported similarly or slightly better for large trials than for small trials (data not shown). The largest difference was seen for the nomination of a primary outcome (13/24, 54% of large and 13/46, 28% of small trials). Results for other reporting items are available in the Table, Supplemental Digital Content 2, https://links.lww.com/INF/B335. The numbers randomized to each group were fully reported in 69% of publications, losses and exclusions after randomization in 50% and reasons for losses and exclusions in 34%. In the 18 publications that stated both intention-to-treat and per-protocol analyses were conducted, 11 (61%) stated clearly which analysis was used for each set of results. Of the 26 publications that nominated a primary outcome, 21 (81%) reported a point estimate and confidence interval for a measure of effect.
Reporting of Additional Vaccine-related Items
The intended ages at vaccination were reported in all 54 publications about childhood vaccination, either as exact ages or age ranges. The actual ages at which each vaccine dose was administered were, however, reported fully in only 11 (20%) of these publications. In the journals with the most publications included in this review, this item was fully reported in 3 (18%) publications in Pediatric Infect Dis J and 1 (7%) in Vaccine. Actual ages at vaccination were fully reported in 40% (6/15) of large trials and 13% (5/39) of small trials.
In this study of publications about 3 vaccines, the number of individuals included in primary outcome analyses, the intended ages at vaccination and trial registration numbers were well reported. Trials were infrequently identified as randomized in the title and the allocation concealment methods, the groups who were blinded and the actual ages at vaccination were often not fully reported.
A strength of this study is the selection of both established and more recent vaccines, which allowed us to examine the completeness of reporting in both older and more recent trials. A further strength is the assessment of all publications by 2 reviewers to minimize the potential for classification errors. The main limitation of this study is the small sample size. A total of 70 RCTs had low statistical power for making formal statistical comparisons over time or between journals, but is not dissimilar to other subject-specific reviews of reporting completeness.35,37,39,40 Nevertheless, the descriptive analysis provides important information about overall levels of adherence to the CONSORT statement. Another limitation is that we examined reporting in published trials of only 3 vaccines. This study, therefore, covers only a small proportion of all RCTs for currently licensed vaccines, which target around 30 pathogenic viruses and bacteria,43 and there might be differences in completeness of reporting for other vaccines. However, the 2 childhood vaccines under consideration were licensed relatively recently, and we would not expect marked differences in the reporting of other vaccine trials in the same era. We located some journal publications of included studies by using their trial registration number and this might overestimate how many trials reported this number. We were also unable to examine improvements after journals endorsed CONSORT because it was not possible to obtain the date of first endorsement by each journal.
To our knowledge, this is the first study investigating adherence to the CONSORT statement in vaccine research. The largest study examining the completeness of reporting compared RCTs published in all areas of health research in 2000 with those published in 2006.36 Our findings were in line with those for all RCTs. Vaccine trials can, therefore, not be assumed to be better reported than other trials in health research. For vaccine-related studies, a systematic review of vaccine safety data in publications from 1995 to 2000 showed that more prelicensure studies reported on safety than postlicensure studies.39 Another study of efficacy, immunogenicity or phase I clinical vaccine trials published in 1991 to 1992 concluded that the reporting of factors such as vaccination technique and technical factors affecting vaccine response was not optimal.40
There are several possible reasons for incomplete reporting of the methods and results of RCTs. Low awareness about the need for detailed descriptions about randomization methods has been noted before.44 Limits to the maximum length of journal articles might also be thought to make it difficult to give detailed explanations. In our study, however, several items appeared to be more completely reported in the small number of publications in The Lancet, which has a limit of 3000 words, than in Vaccine or Pediatr Infect Dis J, which do not specify a limit. Similarly, large trials tended to be better reported than small trials, although they were also most frequently published in journals with strict word limits.
RCTs of vaccines that are completely reported can contribute more to decisions about their introduction and use if they can be found and their methods can be fully assessed. The items in the checklist are treated equally because they provide information that is important for different reasons. Publications are easier to find in a literature search if they are clearly signposted as RCTs in the title, and the results are easier to interpret if they contain details that can be compared with other trials. Complete reporting also allows the reader to assess the extent and direction of bias that might be present in a trial. For example, in the absence of blinding, bias is unlikely for objective outcomes such as mortality whereas overestimations of effect are often seen for subjective outcomes such as clinical pneumonia or disease severity.7 Processes such as Grades of Recommendation Assessment, Development and Evaluation are likely to downgrade the quality of evidence if there are few trials identified and reporting is incomplete; the strength of recommendations for the use of a vaccine could be weakened as a result.
Editorial mechanisms can be very successful in improving the quality and completeness of the research evidence by enforcing requirements for article submission. For example, the International Committee of Medical Journal Editors has helped to implement prospective registration of RCTs by requiring registration in a public trials registry as a condition of publication since 2004.45 High levels of compliance with this requirement have been achieved, as shown in our study and others.46,47 Other CONSORT reporting items are still incompletely reported in vaccine trial publications. Neither of the 2 most prolific publishers of vaccine trials endorsed CONSORT at the time of this study nor requested the submission of a completed CONSORT checklist with manuscripts about RCTs. These journals could take a lead role in improving the completeness of reporting of vaccine trials. Journal editors can provide easily accessible resources for authors on their websites and install mechanisms to ensure that reporting guidelines have been followed. This study provides baseline data for key reporting items so that the impact of changes in editorial policy can be monitored. Instructions for authors should include guidance about how to prepare their manuscript in adherence to the CONSORT statement, with links to the CONSORT checklist and flow diagram. The CONSORT group also publishes an open access “explanation and elaboration” document, which has excellent examples of how each item can be well reported.14 The Enhancing the QUAlity And Transparency of health Research (EQUATOR) network website is a portal for resources for authors, reviewers and editors.31
This study found that the completeness of reporting of RCTs of vaccine effects could be improved. Editors of journals that publish vaccine-related RCTs could take a lead by implementing initiatives such as the Brighton Collaboration checklist for reporting vaccine safety,48 and the development of a list of vaccine-specific trial characteristics,49 in addition to endorsing the CONSORT statement. Changes in the submission process to improve reporting would make RCTs of vaccines easier to find, the findings easier to interpret and would aid the incorporation of findings into policy and practice.
The authors thank Ekaterina Safroneeva and Darja-Anna Yurovsky for their assistance in assessing the Russian language publication. PS, FO and NL designed the study. PS and FO selected the studies, extracted the data and performed the statistical analyses. PS, FO, ME and NL contributed to the interpretation of the data, revised the manuscript critically and approved the final version.
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