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

Abstract

Objective: 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 to August 2024.

Methods: A cost-utility analysis was performed using a Markov model from the healthcare system perspective for three different age groups (18 - 64; 65 - 74; and ≥ 75 years). Costs and outcomes with the monovalent XBB.1.5 vaccine were compared to no updated booster dose for one year. Health outcomes were expressed as Quality-adjusted life-years (QALY), while 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 AU$50,000/QALY.

Results: The updated vaccine was dominant for the 18 - 64 years group, and cost-effective for the 65 - 74 years group (incremental cost-effectiveness ratio [ICER] = AU$10,786/QALY), and ≥ 75 years group (ICER = AU$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 non-indigenous Australians. The results were robust to simultaneous changes in the parameters' values.

Conclusion: 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.