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.

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