Issues in the economic evaluation of influenza vaccination by injection of healthy working adults in the US: a review and decision analysis of ten published studies.

The objective was to review recent economic evaluations of influenza vaccination by injection in the US, assess their evidence, and conclude on their collective findings. The literature was searched for economic evaluations of influenza vaccination injection in healthy working adults in the US published since 1995. Ten evaluations described in nine papers were identified. These were synopsized and their results evaluated, the basic structure of all evaluations was ascertained, and sensitivity of outcomes to changes in parameter values were explored using a decision model. Areas to improve economic evaluations were noted. Eight of nine evaluations with credible economic outcomes were favourable to vaccination, representing a statistically significant result compared with a proportion of 50% that would be expected if vaccination and no vaccination were economically equivalent. Evaluations shared a basic structure, but differed considerably with respect to cost components, assumptions, methods, and parameter estimates. Sensitivity analysis indicated that changes in parameter values within the feasible range, individually or simultaneously, could reverse economic outcomes. Given stated misgivings, the methods of estimating influenza reduction ascribed to vaccination must be researched to confirm that they produce accurate and reliable estimates. Research is also needed to improve estimates of the costs per case of influenza illness and the costs of vaccination. Based on their assumptions, the reviewed papers collectively appear to support the economic benefits of influenza vaccination of healthy adults. Yet the underlying assumptions, methods and parameter estimates themselves warrant further research to confirm they are accurate, reliable and appropriate to economic evaluation purposes.