E-4 INCORPORATING INDIRECT BENEFITS OF VACCINATION INTO COST-EFFECTIVENESS ANALYSIS

Tuesday, October 20, 2009: 1:45 PM
Grand Ballroom, Salon 5 (Renaissance Hollywood Hotel)
Yoko Ibuka, PhD1, Alison Galvani, PhD1 and A. David Paltiel, PhD2, (1)Yale University, New Haven, CT, (2)Yale University School of Medicine, New Haven, CT
Background: Vaccination provides an indirect benefit to unvaccinated individuals, however existent cost-effectiveness analyses on vaccination programs often exclude the indirect benefits of vaccination.

Purpose: We incorporated indirect benefits of vaccination into a cost-effectiveness analysis for vaccination against seasonal influenza by using a mathematical model of disease transmission dynamics. Specifically, we evaluated costs and effectiveness at different vaccination coverage levels to examine how the indirect benefits affect the costs and effectiveness.

Methods: A dynamic epidemiological model of influenza transmission was constructed and parameterized based on the estimates from published literature. Our model assumed a homogeneous random-mixing population of100,000 individuals. Using the model, we evaluated the costs and health outcomes of vaccination program for influenza with various levels of vaccination coverage, ranging 0% to 90% with 10% increments. Effectiveness was measured in terms of the number of influenza cases averted in the population, and the costs include vaccination costs as well as direct medical costs for treatment of influenza. Incremental cost effectiveness ratios (ICERs) were calculated as a comparison to the next best strategy in order to examine additional costs required to avert one infection.

Results: The number of influenza cases averted increased in non-linear fashion as vaccination coverage increased (Figure). 38,211 cases were additionally averted when vaccination coverage increased from 10% to 20%; on the other hand, the additional gain was only 804 cases when the coverage increased from 80% to 90%. In contrast, the costs monotonically increased once the vaccination coverage exceeded 50%. As a result, the ICERs were $1, $84 and $380 per influenza case averted, at 20%, 50%, and 90% vaccination coverage levels, respectively.

Conclusions: The additional gain in the effectiveness of vaccination program could decrease with wider vaccination coverage due to reduced additional indirect benefits from vaccination. Therefore, it is critical to incorporate the indirect benefit of vaccination program into its cost-effectiveness analysis using a dynamic model of disease transmission.

Candidate for the Lee B. Lusted Student Prize Competition