Are Updated COVID-19 Vaccines Still Relevant for All Adult Age Groups? An Economic Evaluation of the Monovalent XBB.1.5 Vaccine in Australia

Objectives There is a progressive decline in the relative effectiveness of updated COVID-19 vaccines. Surveillance reports in Australia have also shown a wide variation in the disease severity and mortality across age groups. This study aimed to perform a cost-utility analysis of the monovalent XBB.1.5 vaccine relative to no updated booster vaccine between September 2023 and August 2024. Methods A cost-utility analysis was performed using a Markov model from the healthcare system perspective for 3 different age groups (18-64, 65-74, and ≥75 years). Costs and outcomes with the monovalent XBB.1.5 vaccine were compared with no updated booster dose for 1 year. Health outcomes were expressed as quality-adjusted life years (QALYs), whereas costs were presented in 2023 Australian dollars. Aggregate distributional cost-effectiveness analysis and sensitivity analyses were performed. The willingness-to-pay threshold was set at A$50 000/QALY. Results The updated vaccine was dominant for the 18 to 64 years group and cost-effective for the 65 to 74 years group (incremental cost-effectiveness ratio [ICER] = A$10 786/QALY) and ≥75 years group (ICER = A$36,531/QALY) relative to no updated booster vaccine. The major determinants of the ICER was the vaccine uptake rate. There was inequality in health benefits between the older First Nations versus nonindigenous Australians. The results were robust to simultaneous changes in the parameters’ values. Conclusions The monovalent XBB.1.5 vaccine is cost-effective and still relevant for all adult age groups in Australia. Based on current evidence, the study findings support the promotion of booster vaccination for Australian adults.