OBJECTIVES : There are two strains of seasonal influenza A and two lineages of seasonal influenza B viruses. Trivalent influenza vaccine (TIV) contains both circulating influenza A strains but only a lineage of influenza B. A quadrivalent influenza vaccine (QIV) was designed to protect against the four influenza viruses. This study assessed the cost-effectiveness of switching TIV to QIV in Portugal.

METHODS : An analytic decision model was developed to estimate the cost-effectiveness of QIV versus TIV for an average influenza season, under the societal perspective. Influenza A strains vaccine efficacy derived from literature estimates. Influenza B vaccine efficacy was calculated as a weighted average of the efficacy against the matched and mismatched strain derived from data published by the European Centre for Disease Prevention and Control. Vaccine coverage and influenza-related outcomes derived from national data. A 5% annual discount rate was adopted for costs and effects following Portuguese guidelines. Results were expressed in number of influenza cases, influenza-related deaths, healthcare resource consumption, productivity losses, incremental costs per life year (LY) and quality adjusted life years (QALY).

RESULTS : On average, seasonal vaccination with QIV is expected to decrease the number of influenza cases by 3,773 and influenza-related deaths by 118 versus TIV. Vaccination with QIV is expected to augment overall vaccination costs by 4,169,484€, offset by 2,068,275€ saved in healthcare resource consumption and productivity losses. QIV adoption is expected to represent a gain of 1,089 LY and 1,038 QALY. The corresponding incremental CE ratio is 1,929€/LY and 2,041€/QALY. The probabilistic sensitivity analysis confirmed a 96.5% probability of QIV to be a cost-effective strategy for a 20,000€/QALY willingness to pay.

CONCLUSIONS : Vaccination of the Portuguese population with QIV is expected to provide a clear benefit in terms quality of life and survival, at an incremental cost per LY and QALY gained over TIV, within an acceptable range.