Cost-effectiveness of inactivated influenza vaccination in children with medical risk conditions in the Netherlands

Background: In many countries, annual immunization with inactivated influenza vaccine (IIV) is recommended for children with medical risk conditions. Prior cost-effectiveness analyses found such immunization to be cost saving, but assumed effectiveness against non-severe influenza outcomes and a higher effectiveness against severe influenza outcomes than recent studies would suggest. However, recent vaccine studies do not indicate any reduction in community or outpatient disease episodes in IIV immunized individuals. We therefore evaluated cost-effectiveness of IIV immunization in children with medical risk conditions in the Netherlands, assuming that IIV reduces influenza-related hospitalization and death, but has no meaningful impact on non-severe health outcomes. Methods: A health economic decision tree model was developed to evaluate health effects and costs of annual IIV immunization versus no immunization. Model inputs were based on our study on influenza-related primary care visits and other literature. Immunization was considered cost effective if associated costs were less than €20,000 per quality-adjusted life year (QALY) gained. Probabilistic sensitivity analyses were performed to assess robustness of results, and one-way sensitivity analyses and scenario analyses were done to assess the influence of individual parameters. Results: Annual IIV prevents an average of 1.59 influenza-related hospitalizations and 0.02 deaths per 1,000 children with medical risk conditions. This results in an expected QALY gain of 0.43 at incremental costs of €21,564 per 1,000 children, corresponding to an incremental cost-effectiveness ratio (ICER) of €50,297/QALY compared to no immunization. Under base case assumptions, immunization had a 5% probability of being cost effective. Results were most influenced by vaccine efficacy against fatal influenza, QALY loss due to death, and mortality rate. Conclusions: If IIV only reduces severe disease outcomes, as current evidence suggests, annual immunization of medical risk children is unlikely to be cost effective. Results should however be interpreted with caution as cost-effectiveness is largely dependent on incidence and QALY losses for fatal influenza, for which evidence is scarce