Gap between policy and evidence
The large gap between policy and what the data tell us (when rigorously assembled and evaluated) is surprising. The reasons for this situation are not clear and may be complex. The starting point is the potential confusion between influenza and influenza-like illness, when any case of illness resembling influenza is seen as real influenza, especially during peak periods of activity. Some surveillance systems report cases of influenza-like illness as influenza without further explanation. This confusion leads to a gross overestimation of the impact of influenza, unrealistic expectations of the performance of vaccines, and spurious certainty of our ability to predict viral circulation and impact. The consequences are seen in the impractical advice given by public bodies on thresholds of the incidence of influenza-like illness at which influenza specific interventions (antivirals) should be used.20
The confusion between influenza and influenza-like illness is compounded by the lack of accurate and fast surveillance systems that can tell what viruses are circulating in a setting or community within a short time frame, and after the "season" is finished give an accurate picture of what went on to enable better forecasting of future trends.21 Accurate surveillance must be based on a properly worked out sampling system for cases of influenza-like illness that meet set criteria, with accurate and quick feedback of a presumptive microbiological diagnosis. Without this, we cannot generalise from random sampling.
Another reason may be "availability creep." In their efforts to deal with, or be seen to deal with, policy makers favour intervention with what is available—registered influenza vaccines. A similar philosophy is the "we have to make decisions and cannot wait to have perfect data" approach. This attitude may have an altruistic basis but has two important consequences. Firstly, it uses up resources that could be invested in a proper evaluation of influenza vaccines or on other health interventions of proven effectiveness. Secondly, the inception of a vaccination campaign seems to preclude the assessment of a vaccine through placebo controlled randomised trials on ethical grounds. Far from being unethical, however, such trials are desperately needed and we should invest in them without delay. A further consequence is reliance on non-randomised studies once the campaign is under way. It is debatable whether these can contribute to our understanding of the effectiveness of vaccines. Ultimately non-randomised designs cannot answer questions on the effects of influenza vaccines.
