Smallpox is the only disease that has been eradicated in humans, thanks in part to the bifurcated needle. It holds a dose of reconstituted smallpox vaccine in its prongs and punctures a person’s skin easily to the ideal depth for delivery. The needle was a cost-effective alternative to a clunky, unreliable jet injector that had been slowing down vaccination campaigns. Between 1966 and 1977, a World Health Organization program led by D.A. Henderson, who later became dean of what is now the Johns Hopkins Bloomberg School of Public Health, used the needle to aid delivery of more than 200 million smallpox vaccinations a year and eradicate the dreaded disease.