A systematic review of health state utility values for influenza and influenza-like illness

Health economic evaluations commonly rely on quality-adjusted life years (QALYs) to measure healthcare intervention effectiveness, calculated by assigning quality weights to the time people spend in disease-specific health states. Influenza and influenza-like illness (ILI) compromise people’s health-related quality of life (HRQoL), but comprehensive overviews on influenza or ILI-associated quality weights are still scarce. This systematic literature review provides an overview of studies that estimated influenza and ILI effects on HRQoL expressed as health state utility values (HSUVs). We conducted a systematic literature review in MEDLINE and Embase to capture published utility values associated with influenza and ILI in all age groups. We restricted our review to studies published between January 1990 and mid-August 2023. Quality assessment was carried out using 10 pre-defined questions. We included 25 studies published between 1997 and 2022 conducted in Europe, North America, Asia, and Australia. The studies used a variety of preference-based and rating scale measures to derive utilities for influenza and ILI patients—variations of the EQ-5D were most frequently used. For the worst day of illness, elicited utility scores ranged from −0.342 in patients with laboratory-confirmed influenza to 0.48 in patients with ILI. Observed differences between values could be attributed to differences between assessed groups (e.g. inpatient vs. outpatient population) and timepoints (e.g. worst day of illness). We identified only one study reporting values for different age groups. Study quality differed overall, with only 6 studies fulfilling all pre-defined and applicable quality criteria. We found varying study conduct and HSUV elicitation methods which led to heterogenous HSUVs assigned to influenza and ILI in identified studies. Limited applicability of existing HSUVs for influenza should be factored into decision making processes as they might not represent targeted populations in cost-utility analysis.