OBJECTIVES: In publicly-funded vaccination programmes, vaccine costs are often confidential and negotiated following a policy decision to offer vaccination. In economic evaluations, vaccine costs must therefore be assumed, creating considerable uncertainty in the results. This study aimed to develop automated decision rules as part of an economic evaluation, enabling the payer to identify the optimal vaccination strategy once vaccine prices are known.

METHODS: A cost-utility analysis of influenza vaccination for Ireland was used, comparing three vaccination strategies employing a standard, adjuvanted or high-dose inactivated influenza vaccine. Vaccine costs were assigned uniform distributions within plausible ranges and varied simultaneously in probabilistic simulations. Vaccine costs ranged from €5 to €10.99 for standard, €10.99 to €25 for adjuvanted, and €10.99 to €45 for high-dose, with the additional assumption that high-dose was always more costly than adjuvanted. For each simulation, the net monetary benefit (NMB) was determined for each strategy at a willingness-to-pay threshold of €20,000 per QALY. Recursive partitioning was used to derive decision rules for identifying the strategy with the largest NMB based on the vaccine costs.

RESULTS: The rules were developed using a training dataset of 5,000 simulations. Appling them to a validation dataset achieved correct identification of the optimal strategy in 87% of cases. The following decision rules were generated:

• High-dose is optimal if the vaccine cost is ≤ €9.40 greater than adjuvanted AND adjuvanted is ≤ €9.60 greater than standard.
• Adjuvanted is optimal if the vaccine cost is ≤ €6.40 greater than standard AND high-dose is > €9.60 more than adjuvanted.
• Standard is the optimal in all other situations.

CONCLUSIONS: When comparing vaccination strategies in economic evaluations, automated decision rules around vaccine costs can be developed using recursive partitioning. Those rules can enable payers to easily identify the optimal vaccination strategy based on NMB when negotiating vaccine prices with manufacturers.