OBJECTIVES: This research aims to assess the economic impact and cost-utility of replacing trivalent inactivated influenza vaccines (IIV3) with the newer influenza vaccines – trivalent high dose (HD) or quadrivalent (IIV4) influenza vaccine in adults aged 65 and older under Ontario’s Universal Influenza Immunization Program (UIIP) from healthcare and societal perspectives.   METHODS: An analytical decision model was developed for the elderly (age 65-74, 75-84, and 85 and above) at two levels of health risks (high and low) with influenza-related health outcomes from Ontario or Canada.  Ontario’s demographic data and labor costs were extracted from Statistics Canada.  Vaccine efficacies were based on post-marketing clinical study for HD and estimated from published literatures for IIV4.  Antiviral treatment and over-the-counter medication costs were considered.  Deterministic (DSA) and probabilistic sensitivity analyses (PSA) were conducted.  Additional analysis was performed for long-term impact of influenza infections.   RESULTS: Comparing to IIV3 under UIIP, IIV3 HD has a net societal budget impact of C$346,809 including premature deaths in a single influenza season.  The incremental cost-effectiveness ratio (ICER) is C$3,763 per QALY gained from healthcare perspective and C$190 per QALY gained from societal perspective.  Replacing IIV3 with IIV4 would result a net societal budget impact of over C$3 million.  The ICER of IIV4 vs IIV3 is C$20,733 per QALY gained from healthcare perspective and societally C$16,232 per QALY gained.  At $50,000 per QALY gained threshold, 100% and 93.8% of PSA simulations were cost-effective for HD and IIV4, respectively, from healthcare perspective, and 95.3% for IIV4 from societal perspective.  HD becomes a dominant alternative when long-term care costs are considered.   CONCLUSIONS: Both HD and IIV4 are expected to reduce influenza-associated morbidity and mortality, and are cost-effective in the studied population comparing to IIV3; however, IIV4 is extended dominated by HD.  Those conclusions were proven to be robust in sensitivity analyses.