Influenza vaccination: policy versus evidence

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Abstract
Policies Every vaccination campaign has stated aims against which its effects must be measured. The US Advisory Committee on Immunisation Practices produces a regularly updated rationale for vaccination against influenza.1 The current version identifies 11 categories of patients at high risk of complications from influenza (box). The rationale rests on the heavy burden that influenza imposes on the population and the benefits of vaccination. For example, reductions in cases, admissions to hospital, mortality of elderly people in families with children, contacts with healthcare professionals, antibiotic prescriptions, and absenteeism for children and household contacts are the main arguments for extending vaccination to healthy children aged 6-23 months in the United States.2 Canada introduced a similar policy in 2004.3 Less comprehensive policies recommending vaccination for all people aged 60 or 65 and over are in place in 40 of 51 developed or rapidly developing countries.4 On the basis of single studies, the World Health Organization estimates that “vaccination of the elderly reduces the risk of serious complications or of death by 70-85%.”5 Given the global nature of these recommendations, what type of evidence should we expect to support them and what does available evidence tell us?4