Relation of study quality, concordance, take home message, funding, and impact in studies of influenza vaccines: systematic review

BMJ 2009; 338 doi: (Published 12 February 2009) Cite this as: BMJ 2009;338:b354
  1. T Jefferson, coordinator,
  2. C Di Pietrantonj, statistician,
  3. M G Debalini, researcher,
  4. A Rivetti, researcher ,
  5. V Demicheli, director of health, Piemonte region
  1. 1Cochrane Vaccines Field, ASL (Azienda Sanitaria Locale) AL 20, 15100 Alessandria, Italy
  1. Correspondence to: T Jefferson jefferson.tom{at}
  • Accepted 3 November 2008


Objective To explore the relation between study concordance, take home message, funding, and dissemination of comparative studies assessing the effects of influenza vaccines.

Design Systematic review without meta-analysis.

Data extraction Search of the Cochrane Library, PubMed, Embase, and the web, without language restriction, for any studies comparing the effects of influenza vaccines against placebo or no intervention. Abstraction and assessment of quality of methods were carried out.

Data synthesis We identified 259 primary studies (274 datasets). Higher quality studies were significantly more likely to show concordance between data presented and conclusions (odds ratio 16.35, 95% confidence interval 4.24 to 63.04) and less likely to favour effectiveness of vaccines (0.04, 0.02 to 0.09). Government funded studies were less likely to have conclusions favouring the vaccines (0.45, 0.26 to 0.90). A higher mean journal impact factor was associated with complete or partial industry funding compared with government or private funding and no funding (differences between means 5.04). Study size was not associated with concordance, content of take home message, funding, and study quality. Higher citation index factor was associated with partial or complete industry funding. This was sensitive to the exclusion from the analysis of studies with undeclared funding.

Conclusion Publication in prestigious journals is associated with partial or total industry funding, and this association is not explained by study quality or size.


  • Karen Davies, Peter Doshi, Peter Gøtzsche, and Iain Chalmers commented on previous drafts.

  • Contributors: TJ, CDP, and VD designed the study. TJ and CDP wrote the protocol. AR and MGD carried out supplementary searches. TJ, AR, and MGD applied inclusion criteria and extracted data. CDP checked data extraction and carried out data analysis and statistical testing. TJ, CDP, and VD wrote the final report. All authors contributed to both protocol and final report. VD is guarantor.

  • Funding: This study was funded by ASL AL, Alessandria, Piemonte, Italy. The funding source had no role in the study design, collection, analysis, and interpretation of results, in the writing of the report, or in the decision to submit the paper for publication.

  • Competing interests: TJ owned shares in GlaxoSmithKline and has received consultancy fees from Sanofi-Synthelabo (2002) and Roche (1997-9).

  • Ethics approval: Not required.

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