No surprises!

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T Jefferson, coordinator, C Di Pietrantonj, statistician, M G Debalini,

researcher, A Rivetti, researcher , V Demicheli, director of health, Piemonte

region

1 Cochrane Vaccines Field, ASL (Azienda Sanitaria Locale) AL 20, 15100

Alessandria, Italy

Correspondence to: T Jefferson jefferson.tom{at}gmail.com

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.

© Jefferson et al 2009

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