OBJECTIVES: Influenza causes annual epidemics whose clinical and economic impacts show large seasonal variability. Although quadrivalent influenza vaccines (QIVs) provide broader protection against circulating influenza B lineages, use of trivalent influenza vaccines (TIVs) in the United States (US) persists. The objective of this study was to estimate the clinical and budgetary impact of converting remaining TIV market share to QIV in the US, while accounting for influenza’s seasonal epidemiologic variability more precisely than previous models.
METHODS: A budget-impact model was constructed using season-specific epidemiological parameters (e.g., attack rates, hospitalization rates) derived from Centers for Disease Control and Prevention published data for eight recent seasons; previous modeling approaches used average parameter values across seasons, including average attack rates from vaccine clinical trials conducted over limited seasons. The base-case estimates the annual budget impact (2016 US$) of converting 100% of current TIV market share to QIV in the US population aged =6 months. Influenza cases prevented were estimated using 2015/2016 vaccine coverage estimates, as well as influenza A/B type-specific vaccine efficacy data. Influenza-related outcomes and costs were then estimated using a decision-tree framework. Scenario analyses considered different payer perspectives and TIV market share conversions.
RESULTS: Using mean parameter values across the eight influenza seasons, converting TIV market share to QIV resulted in 84,272 fewer influenza cases, 1,354 fewer hospitalizations, and 67 fewer deaths annually, with a corresponding budget impact of $0.013 per-person per-month (PPPM). Results varied substantially based on the epidemiological data from individual seasons, ranging from 211,557 fewer influenza cases and a PPPM cost of $0.001 using data from 2007/2008 to 11,904 fewer influenza cases and a PPPM cost of $0.025 using data from 2006/2007.
CONCLUSIONS: The model estimated that conversion of TIV to QIV results in decreased clinical burden and deaths while slightly increasing costs. Using season-specific epidemiological inputs demonstrated outcome variability by season.
