Objective: To estimate the numbers of healthcare encounters and healthcare costs attributable to influenza viral strains A and B in the US during the 2001/2002 – 2008/2009 seasons.
Methods: An Excel model was developed to estimate healthcare encounters and costs in the US during the 2001/2002 – 2008/2009 seasons for influenza type A and type B separately and collectively, by season, care setting, and age group. Rates of influenza-related encounters requiring formal healthcare, unit costs of influenza-related healthcare encounters, and estimates of population size were based on data from published literature, data on file, and secondary sources (GSK ID: HO-13-12299).
Results: The projected annual number of influenza-related healthcare encounters ranged from 11.3 million (2008/2009) to 25.6 million (2007/2008), with a mean of 17.3 million. Overall healthcare costs ranged from $2.0 billion (2008/2009) to $5.8 billion (2007/2008); mean cost was $3.5 billion. Outpatient visits accounted for 99% of all encounters, and almost two-thirds of healthcare costs. While the majority of disease was attributable to type A, type B influenza accounted for 4.2% (2003/2004) to 63.8% (2002/2003) of all influenza-related healthcare encounters, and 2.8% (2003/2004) to 66.0% (2002/2003) of influenza-related healthcare costs; corresponding mean percentages over all seasons was 40.8% and 37.0%, respectively. The percentage of influenza-related healthcare encounters attributable to type B infection was higher in the outpatient setting (40.9%) than in the inpatient setting (27.8%).
Conclusion: Influenza was associated with substantial clinical and economic burden. Although the fraction of this burden attributable to type B disease varied substantially across years, it was, on average, responsible for 37% of total influenza-related healthcare costs. Increasing influenza vaccine coverage, especially with the recently approved quadrivalent products that include an extra type B strain, may significantly reduce the overall annual burden of influenza in the US.
GlaxoSmithKline Biologicals SA:
S. Sokolowski, GlaxoSmithKline Biologicals SA: Research Contractor , Research support
G. Krishnarajah, GlaxoSmithKline: Employee , Research support