Economic evaluation of supplemental measles immunization at the 7^th and 12^th grades in Japan

Abstract

Recently, there have been reports in Japan of measles infection among individuals who had been vaccinated against the disease in their childhood. Possible reasons for such reinfection are : 1) primary vaccine failure (PVF), the failure to develop immunity after vaccination; and/or 2) secondary vaccine failure (SVF), a decrease in immunity due to waning antibodies after vaccination. In response to these cases, the Japanese government has decided to provide supplemental measles immunization for non-infected children in the 7^th grade and 12^th grade for 5 years starting in 2008. Vaccines are one of the most cost-effective interventions in health programs, and this policy is expected to reduce the number of measles patients. However, the cost-effectiveness of supplemental immunization greatly depends on the age at which it is administered. The present study aims to evaluate the cost-effectiveness of supplemental measles immunization at the 7^th and 12^th grades compared with the absence of supplemental immunization.
In the present study, cost-effectiveness is measured by the incremental cost effectiveness ratio (ICER), which denotes the necessary cost of 1 year of good health. Costs are measured in terms of the social health expenditures , and health effects are represented by quality adjusted life years (QALYs). A decision tree and a Markov model were developed to estimate the costs and health effects associated with the supplemental immunization. The time horizon was set at 50 years, and a discount rate was adopted. We then adopted the criterrion that the intervention is costeffective if the ICER is less than the willingness to pay (WTP), which was 5 million yen per QALY gained.
In the base-case analyses, the ICER at 7^th grade was estimated to be 56.51 million yen per QALY gained, and that at 12^th grade was 283.23 million yen per QALY gained. In both cases, the costs per QALY gained remained over the cost-effectiveness threshold. The sensitivity analyses confirmed the robustness of these results.
The present study thus indicates that supplemental measles immunization vaccine at the 7^th and 12^th grades is not a cost-effective public health intervention in Japan.