The new vaccine proved amazingly powerful in protecting cattle, even when they were injected with 1,000 times a fatal dose of rinderpest. And it met all of Yilma’s criteria for simplicity and heat stability. Requiring no syringes or needles, the vaccine could easily be scratched onto the neck or abdomen of the animal, producing sufficient immune response to ward off the rinderpest virus. Later, the herder could just peel the scab from an animal’s immunization site, grind it up in a saline solution and, from a single calf, have 250,000 additional doses for future vaccinations.

It took just one year to devise the vaccine and another year to move it through animal trials, but it would take the balance of a decade for the vaccine to clear the political hurdles and gain approval for use in Africa.

“It was the first recombinant vaccine to be released in a foreign country by a U.S.-funded researcher, and there was a lot of fear — political fear,” Yilma recalls.

There also was money to be lost by some northerners, particularly the British, whose colonial past left them with a corner on the tropical medicine industry. Yilma still refers to those who tried to obstruct his rinderpest efforts as “the Mafia.”

With a blend of charm, savvy and bulldog tenacity, Yilma maneuvered his way through the regulatory morass. He needed approval not only from U.S. and African officials, but also from international agencies such as the World Health Organization, the Food and Agricultural Organization and the Office Inernationale des Epizooties, an international organization that deals with animal health issues. Even scientists on the biosafety screening committees were leery of the impact a genetically engineered vaccine might have on the environment.

They were also concerned that herders administering the vaccine might accidentally scratch themselves and get a dose of the vaccine, which carried the live, although weakened, vaccinia virus. For people with weakened immune systems, perhaps caused by the AIDS virus, the vaccinia virus that serves as the basis for the rinderpest vaccine might prove lethal, the critics suggested.

Yilma did not share their fears but nevertheless acquiesced and inactivated two of the genes in the vaccine’s vaccinia virus, weakening it enough to prevent any adverse effects for humans. A recent risk-assessment study of the vaccine indicates that the chance of a person being accidentally inoculated with the vaccinia virus is literally about one in a billion.

Finally, in 1993, Yilma received permission to field-test the vaccine in quarantined facilities in both Kenya and Ethiopia. Results from those trials showed that the rinderpest vaccine provided protection for at least 16 months and probably for life.

“Most scientists would have given up,” says Bennie Osburn, dean of the UC Davis School of Veterinary Medicine. “But Yilma persisted.”