The impact of indirect (herd) protection on the cost-effectiveness of pneumococcal conjugate vaccine.

BACKGROUND: The heptavalent pneumococcal polysaccharide-protein conjugate vaccine (PCV7) confers protection against invasive pneumococcal disease (IPD) caused by serotypes that are responsible for substantial morbidity and mortality throughout the world. In 2000, the 7 serotypes covered by PCV7 accounted for 80% to 90% of serotypes isolated from the blood or cerebrospinal fluid of children aged <6 years in the United States. A previous review of the literature spanning the years 1998 to 2005 pertaining to the incidence of IPD among nonimmunized individuals in countries with universal PCV7 immunization suggested an indirect protective effect (herd protection, or community immunity) after widespread vaccination. Consideration of indirect protection against IPD may enhance cost-benefit evaluations of vaccination programs.

OBJECTIVE: The objective of this analysis was to review the literature on cost-effectiveness analyses of PCV7 vaccination to determine whether inclusion of the indirect effect in decision-analysis models substantially affects the cost-effectiveness findings in favor of vaccination.

METHODS: A literature review of cost-effectiveness analyses of PCV7 vaccination was conducted using the DIMDI (Deutschen Institut fur Medizinische Dokumentation und Information) superbase, which comprises 12 databases, to identify articles published between January 2000 and October 2006 using the search terms 7-valent pneumococcal conjugate vaccine AND herd immunity/herd effect, and 7-valent pneumococcal conjugate vaccine AND cost-effectiveness, cost-utility, or cost-benefit analyses. Monetary values were converted to euros and inflated to 2006 values, and events avoided were converted to rates per 100,000 vaccinated to allow comparison across studies. The sensitivity analyses from the models that included indirect effects were examined.

RESULTS: There was wide variability in the health-economic results of the 16 studies that met the inclusion criteria. In studies that did not include indirect effects, the adjusted cost per life-year gained ranged from cost saving to euro140,723 from the societal perspective and from euro56,724 to euro324,218 from the payer perspective. In the 4 studies that included indirect effects, a significant and consistent improvement was seen in the health-economic results in favor of vaccination with PCV7. No trends in variability across time or geographic region were observed.

CONCLUSIONS: Indirect effects had a significant effect on cost-effectiveness, as seen in the sensitivity analyses. Future models should include indirect effects in evaluating the cost-effectiveness of PCV7.