OBJECTIVES: Patients’ health-related quality of life (HRQoL) can be expressed as health state utility values (HSUVs). Although influenza and influenza-like illness (ILI) impair HRQoL, comprehensive summaries on the existing HSUV associated with an influenza or ILI infection are scarce. The objective of this systematic review is to give an overview of studies on HSUVs assigned to influenza and ILI to assess the impact of these conditions on HRQoL.

METHODS: A systematic literature search was performed in the scientific databases MEDLINE and Embase using a predefined search string to identify full-text articles published from 1990 to 2023 and reporting data on influenza and ILI HSUVs. Additionally, a quality assessment consisting of ten self-defined questions was performed.

RESULTS: In total, 25 studies published between 1997 and 2022 were included. These studies utilized a variety of methods to elicit utility weights, with different versions of the EuroQoL 5-item scale (EQ-5D) being used most frequently. Utility values showed great heterogeneity and ranged, for the worst day of infection, from ‑0.342 in patients with laboratory-confirmed influenza to 0.48 in patients with ILI. Observed differences between values potentially reflect the variety of study populations (e.g., outpatient vs. inpatient) and timepoints of assessment. Only one study reported values for different age groups. The quality of the included studies was diverse and only six studies fulfilled all pre-defined and applicable quality criteria.

CONCLUSIONS: Overall, the included studies highlight the variety of the HSUVs assigned to influenza and ILI. Due to differences in study design, elicitation methods and study quality comparability of HSUVs is limited and should be considered when selecting HSUVs for further analysis (e.g., cost-utility analysis).