OBJECTIVE: To assess and compare direct medical costs (incurred by payers) and indirect productivity losses (incurred by employers) associated with influenza seasons with matched or mismatched circulating and vaccine containing influenza B lineages.
METHODS: A retrospective analysis, using two MarketScan databases, for the years 2000-2009. Each influenza season was categorized as matched or mismatched after comparing that season's circulating influenza B lineage and the vaccine influenza B lineage. Patients selected had at least one diagnosis claim for influenza (ICD-9-CM code 487.xx [influenza] or 488.1 [H1N1]) during an influenza season. We assessed the incidence of influenza (overall and influenza B), influenza-related medical utilization and associated costs, and productivity losses for each season.
RESULTS: The four matched seasons had lower average influenza incidence (overall incidence per 100,000 plan members: 509; 95% confidence interval [CI]: 505-512) than the five mismatched seasons (748; 95% CI: 745-751). The mismatched seasons had lower influenza B incidence (average incidence per 100,000 plan members: 126; 95% CI: 125-128) than the matched seasons (165; 95% CI: 163-167). The average, per-patient, total influenza-related medical costs in the mismatched seasons ($300.83; range: $245.38-$371.58) were approximately $61.00 higher than in the matched seasons ($239.43; range: $201.49-$264.01). The mismatched seasons had greater average per-patient, influenza-related productivity-loss costs than the matched seasons (mean: $237.31 vs. $175.10).
CONCLUSION: CDC data showed that influenza A was the predominant circulating strain during seasons in which the circulating influenza B lineage did not match the vaccine influenza B lineage. This resulted in lower influenza B incidence during the mismatched seasons. However, the average, per-patient, influenza-related direct medical costs and indirect productivity losses were higher during the mismatched seasons. Additional research is required to determine if these higher costs can be attributed to influenza B infections and if the influenza severity varies during mismatched seasons.
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