Cost-Effectiveness of Adjuvanted Influenza Vaccine Compared with Standard and High-Dose Influenza Vaccines for Persons Aged ≥50 Years in Spain

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.