Influenza is a contagious respiratory disease that causes severe illness and death, particularly in elderly populations. Two enhanced formulations of quadrivalent influenza vaccine (QIV) are available in Spain. Adjuvanted QIV (aQIV) is available for those aged 65+ and high-dose QIV (HD-QIV) for those aged 60+. In this study, we used a health economic model to assess the costs and outcomes associated with using aQIV or HD-QIV in subjects aged 65+. Using aQIV instead of HD-QIV to vaccinate an estimated 5,126,343 elderly people results in reductions of 5405 symptomatic cases, 760 primary care visits, 171 emergency room visits, 442 hospitalizations, and 26 deaths in Spain each year. Life-years (LYs) and quality-adjusted LYs (QALYs) increases by 260 and 206, respectively, each year. Savings from a direct medical payer perspective are EUR 63.6 million, driven by the lower aQIV vaccine price and a minor advantage in effectiveness. From a societal perspective, savings increase to EUR 64.2 million. Results are supported by scenario and sensitivity analyses. When vaccine prices are assumed equal, aQIV remains dominant compared to HD-QIV. Potential savings are estimated at over EUR 61 million in vaccine costs alone. Therefore, aQIV provides a highly cost-effective alternative to HD-QIV for people aged 65+ in Spain.

Standard-dose quadrivalent influenza vaccines (QIV) are designed to provide protection against all four influenza strains. Adjuvanted QIV (aQIV), indicated for individuals aged 65+ years, combines MF59^® adjuvant (an oil-in-water emulsion of squalene oil) with a standard dose of antigen, and is designed to produce stronger and longer immune response, especially in the elderly where immunosenescence reduces vaccine effectiveness. This study evaluated the cost-effectiveness of aQIV vs. egg-based standard-dose QIV (QIVe) in the elderly population, from the payer and societal perspective in Spain. A dynamic transmission model, which accounts for herd protection, was used to predict the number of medically attended infections in Spain. A decision tree structure was used to forecast influenza-related costs and benefits. Influenza-related probabilities of outpatient visit, hospitalization, work absenteeism, mortality, and associated utilities and costs were extracted from Spanish and European published literature. Relative vaccine effectiveness (rVE) was sourced from two different meta-analyses: the first meta-analysis was informed by laboratory-confirmed influenza studies only, resulting in a rVE = 34.6% (CI95% 2–66%) in favor of aQIV; the second meta-analysis included real world evidence influenza-related medical encounters outcomes, resulting in a rVE = 13.9% (CI95% 4.2–23.5%) in benefit of aQIV. All costs were expressed in 2021 euros. Results indicate that replacing QIVe with aQIV in the Spanish elderly population would prevent on average 43,664 influenza complicated cases, 1111 hospitalizations, and 569 deaths (with a rVE = 34.6%) or 19,104 influenza complicated cases, 486 hospitalizations, and 252 deaths (with a rVE = 13.9%). When the rVE of aQIV vs. QIVe is 34.6%, the incremental cost per quality adjusted life years (QALY) gained was €2240 from the payer; from the societal perspective, aQIV was cost saving compared with QIVe. If the rVE was 13.9%, the incremental cost per QALY was €6694 and €3936 from the payer and societal perspective, respectively. Sensitivity analyses validated the robustness of these findings. Results indicate that replacing QIVe with aQIV in the Spanish elderly population is a cost-effective strategy for the Spanish healthcare system.

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.