On December 4, 1966, a Sunday, William Foege, an American doctor running a medical mission in Ogoja province in eastern Nigeria, got a radio message from a fellow missionary, Hector Ottomueller: something in a village six or seven miles off the nearest road looked like smallpox. Foege and a colleague rode out on small motorized bicycles, carrying them across streams on footlogs, and confirmed it. The program's vaccine supply was almost gone, and no more was coming for months.
Weeks earlier, the same program had vaccinated roughly ninety-three percent of the town of Abakaliki, a coverage rate that should, by the theory of herd immunity everyone in the field believed at the time, have made an outbreak there nearly impossible. One broke out anyway, almost entirely inside one congregation, the Faith Tabernacle Church, whose members had refused the vaccine. A near-total vaccination rate had told the team nothing about where the disease would actually turn up next.
With too little vaccine left to repeat Abakaliki's approach, Foege went that night to a missionary's house that kept a standing 7 p.m. radio check-in, meant only to confirm nobody had a medical emergency. He divided a map among the missionaries on the circuit and asked each to send runners through every village in their section, asking one question: was anyone sick with smallpox. Twenty-four hours later, the answers came back over the same radios, and for the first time the team had an accurate account of exactly where the disease already was, rather than a guess about where it might be. They spent their last vaccine there, and in three more villages that market and travel patterns suggested the virus was heading next. Within three or four weeks, the outbreak was over.
The regional Ministry of Health let the program try the same method across the whole Eastern Region, a population of about twelve million. By early summer of 1967 the team was closing out the region's last known outbreak, having vaccinated only about one person in sixteen. Days later the region seceded as Biafra, and within weeks a civil war shut the area off completely; Foege would not know for months whether that last outbreak had actually been stopped before the border closed. It had. Smallpox never reappeared there while the fighting lasted.
The method was written up, named "surveillance-containment," and adopted country by country across West and Central Africa over the next three years; the region's last case was found in Nigeria in May 1970. The World Health Organization's own official history of the campaign, written years later by the epidemiologists who ran it, is careful not to credit the method alone: elsewhere in the region mass vaccination had already reached most people before containment teams arrived, and the same technique, tried later in parts of Asia without the same rigor, disappointed until it was reworked. But in Ogoja province in December 1966, the vaccine was almost gone. The map was not.