Abstract
To assess the burden of influenza by age and clinical status and use this to inform evaluations of the age and risk-based influenza vaccination policy in the United Kingdom. Weekly laboratory reports for influenza and 7 other respiratory pathogens were extracted from the national database and used in a regression model to estimate the proportion of acute respiratory illness outcomes attributable to each pathogen. Influenza accounted for ∼10% of the attributed respiratory admissions and deaths in hospital. Healthy children under five had the highest influenza admission rate (1.9/1000). The presence of co-morbidities increased the admission rate by 5.7 fold for 5-14 year olds (from 0.1 to 0.56/1000), the relative risk declining to 1.8 fold in 65+ year olds (from 0.46 to 0.84/1000). The majority (72%) of influenza-attributable deaths in hospital occurred in 65+ year olds with co-morbidities. Mortality in children under 15 years was low with around 12 influenza-attributable deaths in hospital per year in England; the case fatality rate was substantially higher in risk than non-risk children. Infants under 6 months had the highest consultation and admission rates, around 70/1000 and 3/1000 respectively. Additional strategies are needed to reduce the remaining morbidity and mortality in the high-risk and elderly populations, and to protect healthy children currently not offered the benefits of vaccination.
Highlights
Interest in prevention and control of seasonal influenza has heightened in the wake of the recent influenza A(H1N1)v pandemic
A major review of the national programme was recently undertaken in the United Kingdom that resulted in the recommendation for annual influenza vaccination of all children aged 2e16 years.[3]
Estimating influenza disease burden is challenging as symptoms are non-specific and few patients presenting with an acute respiratory illness are routinely investigated for virological evidence of influenza infection
Summary
Interest in prevention and control of seasonal influenza has heightened in the wake of the recent influenza A(H1N1)v pandemic. A major review of the national programme was recently undertaken in the United Kingdom that resulted in the recommendation for annual influenza vaccination of all children aged 2e16 years.[3] This recommendation was based on estimates of the burden of disease by age under the existing programme in those with and without high-risk clinical conditions, and modelling the likely impact of different vaccination strategies on the transmission dynamics of seasonal influenza[4] and the cost effectiveness of these strategies.[3]. Studies in which all patients with acute respiratory illness are tested for evidence of influenza are labour intensive and are usually focused on a particular age range and conducted over a limited number of seasons. This makes disease burden comparisons between age groups difficult. While risk factors in virologically confirmed cases may be ascertained, it is difficult to translate these into relative risks in those with and without underlying chronic conditions in the absence of comparable information on the prevalence of such conditions in the population
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