Reassessing global historical ℛ ₀ estimates of canine rabies

Rabies spread by domestic dogs continues to cause tens of thousands of human deaths every year in low- and middle-income countries. Nevertheless rabies is often neglected, perhaps because it has already been eliminated from high-income countries through dog vaccination. Estimates of canine rabies’s intrinsic reproductive number ( ℛ ₀ ), a metric of disease spread, from a wide range of times and locations are relatively low (values < 2), with narrow confidence intervals. Given rabies’s persistence, this consistently low and narrow range of estimates is surprising. We combined incidence data from historical outbreaks of canine rabies from around the world with in-depth contact-tracing data from Tanzania to investigate initial growth rates ( r ₀ ), generation-interval distributions ( G ), and reproductive numbers ( ℛ ₀ ). We improved on earlier estimates by choosing outbreak windows algorithmically; fitting r ₀ using a more appropriate statistical method that accounts for decreases through time; and incorporating uncertainty from both r ₀ and G in our confidence intervals on ℛ ₀ . Our ℛ ₀ estimates are larger than previous estimates, with wider confidence intervals. These revised ℛ ₀ estimates suggest that a greater level of vaccination effort will be required to eliminate rabies than previously thought, but that the level of coverage required remains feasible. Our hybrid approach for estimating ℛ ₀ and its uncertainty is applicable to other disease systems where researchers estimate ℛ ₀ by combining data-based estimates of r ₀ and G .