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.
McGovern et al. (2026) studied this question.