Cost-effectiveness of canine vaccination to prevent human rabies in rural Tanzania

Abstract

Background: The annual mortality rate of human rabies in rural Africa is 3.6 deaths per 100 000 persons. Rabies can be prevented with prompt postexposure prophylaxis, but this is costly and often inaccessible in rural Africa. Because 99% of human exposures occur through rabid dogs, canine vaccination also prevents transmission of rabies to humans.

Objective: To evaluate the cost-effectiveness of rabies control through annual canine vaccination campaigns in rural sub-Saharan Africa.

Design: We model transmission dynamics in dogs and wildlife and assess empirical uncertainty in the biological variables to make probability-based evaluations of cost-effectiveness.

Data sources: Epidemiologic variables from a contact-tracing study and literature and cost data from ongoing vaccination campaigns.

Target population: Two districts of rural Tanzania: Ngorongoro and Serengeti.

Time horizon: 10 years.

Perspective: Health policymaker.

Intervention: Vaccination coverage ranging from 0% to 95% in increments of 5%.

Outcome measures: Life-years for health outcomes and 2010 U.S. dollars for economic outcomes.

Results of base-case analysis: Annual canine vaccination campaigns were very cost-effective in both districts compared with no canine vaccination. In Serengeti, annual campaigns with as much as 70% coverage were cost-saving.

Results of sensitivity analysis: Across a wide range of variable assumptions and levels of societal willingness to pay for life-years, the optimal vaccination coverage for Serengeti was 70%. In Ngorongoro, although optimal coverage depended on willingness to pay, vaccination campaigns were always cost-effective and lifesaving and therefore preferred.

Limitation: Canine vaccination was very cost-effective in both districts, but there was greater uncertainty about the optimal coverage in Ngorongoro.

Conclusion: Annual canine rabies vaccination campaigns conferred extraordinary value and dramatically reduced the health burden of rabies.

Primary funding source: National Institutes of Health.

Figure 1. Rabies transmission model

Our dynamic compartmental model is stratified by host type. Rabid dogs are linked to human deaths through a probability tree of human health outcomes. The equations governing the movement between classes are given in the Appendix.

Figure 2. Cumulative rabies cases after ten years of annual canine vaccination campaigns at increasing vaccination coverage

Cases are undiscounted.

Figure 3. Component and total costs of rabies control with increasing canine vaccination coverage

Dotted lines, costs due to canine vaccination programs achieving a given coverage level; dashed lines, costs due to human post-exposure prophylaxis in the presence of canine vaccination at a given coverage level; and solid lines, sum of these two costs. All costs are cumulative over ten years.

Figure 4. Cost of vaccination coverage and life-years saved

Points indicate increasing canine vaccination coverage. Smaller points indicate dominated strategies, which achieve fewer health benefits than other strategies of equal or lesser cost. Costs and life-years saved are cumulative over ten years. Please note that the two districts are represented on different scales.

Figure 5. Cost-effectiveness acceptability curves

Curves show the probability that a given canine vaccination coverage is optimal, i.e. providing the largest net health benefit at a given willingness-to-pay threshold. At willingness-to-pay thresholds of $1430/life-year and $4290/life-year, the World Health Organization thresholds for “very cost-effective” and “cost-effective” interventions in Tanzania, optimal annual coverage ranges between 70 - 90% in both districts. These thresholds are indicated by solid vertical lines.