Influenza-related health care utilization and productivity losses during seasons with and without a match between the seasonal and vaccine virus B lineage.

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.