In a fractious world, there is one ­enemy that has had a unique ability to compel people from all countries to lock arms: poliovirus. For more than 15 years, the World Health Organization (WHO) has coördinated mass- immunization campaigns in an effort to eradicate poliovirus, a goal it hopes attain by the end of this year. If this Global Polio Eradication Initiative succeeds, it will join the smallpox eradication program as one of the greatest medical triumphs in history. So there was a great gasp in 2003 when northern Nigeria broke ranks with the rest of the world and banned the polio vaccine, triggering an outbreak that soon spread to 12 neighboring countries – and illustrating once again how easily the virus can take advantage of any chink in our collective armor. Then again, the Nigerian setback may unintentionally have given the initiative the added fuel that it needs to cross the finish line on time.

Since its inception, the polio eradication program has reduced the incidence of paralytic polio by 99 percent, from some 350,000 cases a year to fewer than 1,000. As of 2003, the virus was circulating only in Nigeria and five other countries. But in the middle of that year, Muslim clerics in northern Nigeria denounced the vaccine, claiming it contained hormones intended to sterilize girls or that it was contaminated with HIV. By the fall, northern Nigerian politicians and health ministers had banned the immunization campaigns in Kano and two other states – a move seen as a nod to the prestige of the Muslim clerics and a slap at both the West and the country’s Christian president, Olusegun Obasanjo. By year-end, Nigeria had reported more than 355 polio cases, surpassing India and Pakistan for the first time. “Nigeria is a painful example of the potential impact of vaccine refusal,” says Daniel Salmon of Johns Hopkins University’s Bloomberg School of Public Health.

As cases continued to mount in Nigeria, scientists confirmed that the virus had hopped a few borders and paralyzed a child in Ghana, which had not had a case of polio in three years. Soon, they found evidence of Nigerian-like polio strains in 11 other sub-Saharan African countries that had been polio-free for at least three years and so had scaled back their own mass-immunization campaigns. “When Nigeria began to export virus, the virus found an easy home,” says WHO epidemiologist David Heymann, who heads the Global Polio Eradication Initiative. “The tragedy of Kano is that Africa now has 89 percent of all paralyzed children.”

Although the eradication program has elaborate plans for combatting outbreaks of the virus, combatting an outbreak of anti-vaccination fever presented a much different challenge. “We worked really hard behind the scenes,” says Heymann, who personally called the governor of Kano state every day for three weeks. The eradication program also encouraged the Organization of the Islamic Conference – which represents 57 states with large Muslim populations, including Nigeria – to issue a resolution in October 2003 that urged members to step up their eradication efforts. And in February 2004, the program arranged for a Nigerian commission to visit polio vaccine manufacturers in (predominantly Muslim) Indonesia, as well as South Africa and India.

In July 2004, after three Nigerian government commissions agreed that the polio vaccine was safe, Kano state lifted its ban and agreed to accept vaccine from Indonesia. But the ban had already strained the coffers of the eradication program. Its budget through 2005 is $3 billion, with more than $500 million coming from Rotary International. Heymann estimates that it is still $200 million shy of what’s needed, and he says the Nigerian ban accounts for more than half of that shortfall.

There is a silver lining. “What Kano has done is sensitized a whole new series of partners in eradication,” says Heymann. “In the long term, it’s brought solidarity among Islamic countries.” This is especially important given that four of the countries outside of Nigeria with the biggest polio problems are Pakistan, India, Afghanistan, and Egypt. And because of the setback, 25 African nations agreed to launch the largest immunization campaign ever staged, setting out four months ago to immunize 80 million children. In October 2004, at the start of that cam­paign, Heymann projected that polio cases would start to decrease by January. If WHO finds the funding, he says, it will say good-bye to polio by the end of this year, as planned.

Even if there are no cases of polio by year’s end, several obstacles remain. One revives the old conflict between Albert Sabin and Jonas Salk, the polio vaccine pioneers who dueled each other for decades. The simple-to-use oral vaccine that is the cornerstone of the eradication program contains live, weakened strains of poliovirus that occasionally mutate and regain their ability to cause disease. Developed by Sabin, this vaccine will continue to reintroduce poliovirus to the human population as long as it remains in use. The Salk vaccine, which uses killed virus, does not have this drawback, but it must be injected, and that makes it more difficult and costly to deliver. Although plans call for the world to abandon the live vaccine once wild poliovirus stops spreading, timing this precisely will be tricky and may require strategic use of the killed vaccine.

For now, the biggest challenge is not one of strategy. It is one of will. If humans wanted to stop the circulation of wild ­poliovirus, they could. Yet in a tragic irony, because vaccines work so well, many ­people discount their value. Why get a vaccine for polio, measles, or diphtheria if you rarely, if ever, see those diseases in your community? This ambivalence fertilizes antivaccination movements, which recently have swept through not just Nigeria but also the United States, Europe, and Australia. In each case, vaccine-­preventable diseases have surged. It’s a bizarre dilemma. Medical science has a means to control nature, but in the final analysis, human nature decides our fate.