Vaccine Efficacy, Effectiveness, or Impact: Which One to Choose in Economic Evaluations of Vaccines?

At product launch we have access to vaccine efficacy data from randomized clinical trials to develop our economic evaluations. Later on we may obtain vaccine effectiveness data through case-control studies. What matters most however are vaccine impact data over time. If impact results are different from efficacy and effectiveness data, how do they affect the economic results? We take the example of the monovalent vaccine (RIX4414) against rotavirus disease to evaluate that point. We developed models allowing the use of different vaccine effect data to calculate ICERs. We first calculated the ICER using vaccine efficacy data in a static cohort model with adjustment for herd-effect achieved after reaching the ICER steady state level (8 years). We then adjusted the vaccine input parameters with vaccine effectiveness instead of efficacy in a second analysis over a same evaluation period. The vaccine impact data requires the use of a population model instead. We compare the results of the impact data over a same period of assessment with the previous data. Results indicate as expected that the ICER with vaccine efficacy will be lower than with vaccine effectiveness (+7%) already achieved after 8 years of follow-up. The vaccine impact results heavily depend on the vaccine coverage and consequently on the level of herd effect achieved during the first years post-vaccine introduction. It however results in a higher ICER (+13%) with 86% coverage, and 8 years of follow-up. ICER-results will be different by vaccine effect data selected. Impact data are the closest results to what is happening in real life. It is therefore imperative to select those data as the most relevant to measure the economic value of new vaccines. Impact data will obviously not be available when the vaccine is launched. These results question the methodology of vaccine assessment.