Background: The prevalence of chronic conditions that increase the risk of influenza complications is high among individuals aged ≥50 years, and evidence suggests age-related changes in immune responses to vaccines begin to decline at this age. Persons aged 50–59 years have high rates of influenza infections and are also the most likely age group to be employed. Thus, the burden of influenza is high in this age group. Methods: We investigated the cost-effectiveness of vaccination with an adjuvanted quadrivalent influenza vaccine (aQIV) in a Spanish population aged ≥50 years at high risk of influenza complications. Using a static decision-tree model specifically designed to analyze Spanish data, we calculated incremental cost-effectiveness ratios (ICERs) for aQIV vs. egg-based QIV (QIVe; indicated for any age) and aQIV vs. high-dose QIV (HD-QIV; indicated for persons aged ≥60 years) from payer and societal perspectives. We compared ICERs against a willingness-to-pay threshold of EUR 25,000 per quality-adjusted life year (QALY) gained. The impact of input uncertainty on ICER was evaluated through a probabilistic sensitivity analysis (PSA) and a one-way deterministic sensitivity analysis (DSA). Results: The total incremental cost of vaccination with aQIV was EUR –86,591,967.67, which was associated with gains of 241.02 in QALY (EUR –359,268.05 per QALY gained) and 318.04 in life years (EUR −272,271.37 per life year gain). Compared with the willingness-to-pay threshold of EUR 25,000 per QALY gained, aQIV was the most cost-effective influenza vaccine relative to the combination of QIVe or HD-QIV. These findings were supported by PSA and DSA analyses. Conclusions: In the model, aQIV dominated QIVe and HD-QIV, demonstrating that aQIV use would be cost-saving for persons aged ≥50 years who are at high risk of influenza complications.

Background: There is a high burden of influenza among individuals aged 50–64 years, with the highest rates of influenza infections other than children. The MF59-adjuvanted influenza vaccine (adjuvanted trivalent influenza vaccine [aTIV]/adjuvanted quadrivalent influenza vaccine [aQIV]) is designed to enhance response to vaccination among older adults. Among those aged ≥65 years, adjuvanted vaccine (aTIV/aQIV) has shown to be 14% more effective than standard (TIV/QIV) vaccines. This modeling study aimed to estimate the potential public health impact of aTIV/aQIV over standard influenza vaccines (TIV/QIV) among individuals aged 50–64 years over five influenza seasons. Methods: A static compartmental model was developed based on a Centers for Disease Control and Prevention model. Model inputs included vaccine effectiveness, vaccine coverage, population counts and disease burden estimates. Additional burden averted (symptomatic cases, outpatient visits, hospitalizations, intensive care unit [ICU] admissions, and deaths) was expressed as total incremental cases averted between the vaccines. Sensitivity analyses explored the influence of uncertainties in model input on the results. Results: Across the influenza seasons evaluated, on average each 5% increase in the relative vaccine effectiveness (rVE) of aTIV/aQIV vs. QIV prevented an additional 172,738 symptomatic illnesses, 74,277 outpatient visits, 1832 hospitalizations, 343 ICU admissions, and 105 deaths. This corresponds to an average seasonal incremental burden averted of 15.2%, with a range of 5.9% to 37.2%. Deterministic sensitivity analyses revealed the greatest variability was tied to rVE and burden estimates. Probabilistic sensitivity analyses results were normally distributed. Conclusions: Individuals aged 50–64 years could benefit from use of aTIV/aQIV over TIV/QIV, with an average increase in the number of influenza outcomes prevented of 15.2% per 5% improvement in vaccine effectiveness.