Elsevier

Vaccine

Volume 25, Issue 27, 28 June 2007, Pages 5086-5096
Vaccine

The annual impact of seasonal influenza in the US: Measuring disease burden and costs

https://doi.org/10.1016/j.vaccine.2007.03.046Get rights and content

Abstract

Background

Despite preventive efforts, influenza epidemics are responsible for substantial morbidity and mortality every year in the United States (US). Vaccination strategies to reduce disease burden have been implemented. However, no previous studies have systematically estimated the annual economic burden of influenza epidemics, an estimate necessary to guide policy makers effectively.

Objective

We estimate age- and risk-specific disease burden, and medical and indirect costs attributable to annual influenza epidemics in the United States.

Methods

Using a probabilistic model and publicly available epidemiological data we estimated the number of influenza-attributable cases leading to outpatient visits, hospitalization, and mortality, as well as time lost from work absenteeism or premature death. With data from health insurance claims and projections of either earnings or statistical life values, we then estimated healthcare resource utilization associated with influenza cases as were their medical and productivity (indirect) costs in $2003.

Results

Based on 2003 US population, we estimated that annual influenza epidemics resulted in an average of 610,660 life-years lost (undiscounted), 3.1 million hospitalized days, and 31.4 million outpatient visits. Direct medical costs averaged $10.4 billion (95% confidence interval [C.I.], $4.1, $22.2) annually. Projected lost earnings due to illness and loss of life amounted to $16.3 billion (C.I., $8.7, $31.0) annually. The total economic burden of annual influenza epidemics using projected statistical life values amounted to $87.1 billion (C.I., $47.2, $149.5).

Conclusions

These results highlight the enormous annual burden of influenza in the US. While hospitalization costs are important contributors, lost productivity from missed work days and lost lives comprise the bulk of the economic burden of influenza.

Introduction

Influenza has attained an unprecedented degree of attention in recent years as a result of disruptions in vaccine supply and distribution, and concerns about the nation's ability to respond to an influenza pandemic. Influenza has a long history, however, of causing substantial morbidity and mortality nearly every year. Despite vaccination recommendations targeted to high-risk groups and their contacts, an annual average of 36,000 deaths and over 200,000 hospitalizations occurred during the 1990s [1]. Illness severity and mortality are greatest in high-risk groups, and so are the associated healthcare costs and productivity losses [1]. In addition, costs and lost productivity among non-high-risk groups are not trivial [1], [2]. In order to reduce the burden of influenza, various vaccination strategies have been proposed; most recently the Advisory Committee on Immunization Practices extended the recommendation to include children 24–59 months [1].

Economic considerations are an essential ingredient to effectively guide policy-making for influenza vaccination. Numerous studies have considered the cost effectiveness of influenza vaccination [3], [4], [5]. However, only one previous study systematically estimated the economic impact of influenza in the United States and that study focused on the impact of pandemic influenza [2]. This study estimates the annual impact of seasonal influenza in the US by measuring disease burden and associated medical and indirect costs. Projected costs were estimated by age and risk strata. We examined direct medical expenses to treat the disease and its sequelae as well as indirect costs from lost productivity and lives lost due to premature death. Our estimate of the average cost of an influenza season is based on 2003 US population demographics.

Section snippets

Methods

We used both payer and societal perspectives to estimate the economic burden of influenza in the US. The economic burden of influenza at the population level is a function of the cost per case of influenza and the number of cases. In order to account for variation in costs by age and risk of severe complications from influenza, we estimated costs for five age groups: <5 years, 5–17, 18–49, 50–64, and ≥65. In addition, we distinguished the cost for high-risk and low-risk groups. Finally, we

Results

Consistent with earlier studies, results indicated 24.7 million cases of influenza annually with about 31.4 million attributed outpatient visits based on 2003 population demographics. Case-patients accounted for 334,185 hospitalizations and about 3.1 million hospitalized days (Table 3, Table 4). Days of productivity lost due to illness amounted to 44.0 million (Table 4). We estimated 41,008 deaths in case-patients amounting to 610,656 life years lost; the majority of deaths occurred in the older

Discussion

Our results indicate that the annual economic burden of influenza remains very high. The total annual economic burden of influenza epidemics in the United States across all age groups was $87.1 billion (C.I., $47.2 billion, $149.5 billion) using the VSL method to value lost lives including direct medical costs of $10.4 billion (C.I., $4.1 billion, $22.2 billion). The annual burden per capita ranged between $92 (considering only lost earnings) and $299 (including lost lives). When considered from the

Acknowledgements

We acknowledge the insightful comments of Drs. Andrea Molinari, Martin Meltzer, Abigail Shefer, Fangjun Zhou, and Mary McCauley. Potential conflict of interest: all authors: no conflict. Funding: This research was conducted while the authors were employed by the Centers for Disease Control and Prevention (CDC). N.A. Molinari and I. Ortega-Sanchez are economists at NCIRD; M. Messonnier is lead economist at NCIRD; W. Thompson is a senior epidemiologist at OD-OCSO; P. Wortley is a medical officer

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    Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention, US Department of Health and Human Services.

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