Inactivated influenza vaccines: methods, policies, and politics.

The critical evaluation of existing policies is necessary, but fraught with difficulties. Perhaps the best example of this statement are policies identifying influenza as a worthwhile target for prevention using trivalent inactivated vaccines (TIVs). At a first glance, influenza vaccines are a global intervention and extensive vaccination policies are in place in many countries [1]. Most policy-makers do not dispute the burden of influenza disease and its complications, nor the effectiveness of TIV in dealing with such a burden. However, a suite of Cochrane reviews of the effects of TIV and detailed methodological work [2e5] have cast doubt on the scientific basis of the current consensus. The issue is very complicated, but perhaps the starting point is the clinical similarity between influenza-like illness (a syndrome caused by 200-odd known and unknown microorganisms) and influenza (caused by influenza A and B). In any one year, very few cases of influenza-like illness are actually caused by influenza viruses and as such would be amenable of prevention by specific vaccines. The two are not clinically distinguishable and even periods of known higher influenza virus circulation are not predictive, as other organisms (such as rhinoviruses, RSV and parainfluenza viruses) are co-circulating [6,7]. No one knows what the precise burden of influenza morbidity or mortality is as no surveillance system is capable of distinguishing routinely between influenza and influenza-like illness and no one carries out routine autopsies to identify a microbiological cause of death [8,9]. So, guesswork rules. These simple facts are seldom mentioned to physicians and the media, who are instead told that current measures (e.g, vaccination) are sufficient to control the problem, although no one quite knows the size of the problem and few seem to understand its multiagent nature. Critical evaluation of current evidence of the effects of TIV is also difficult, as Nelson et al. show [10]. Cochrane and other systematic reviews have shown overall poor quality