Eradication plans have been in place for decades // Two vaccines have saved millions of lives // More countries become virus-free each year // But several doors to infection remain wide open.
Still a Scourge
Some of these kids have been vaccinated 10 or 12 times,” says Olen Kew, “and they still get paralytic polio.” For 21 years, Kew, chief of the molecular virology laboratory at the Centers for Disease Control and Prevention in Atlanta, has been involved with the global effort to eradicate polio. His voice cracks in frustration as he recounts the virus’s continued elusiveness even as the campaign, launched by the World Health Assembly in 1988, draws nearer its goal.
Eradicating poliomyelitis has been more difficult and taken more time than almost anyone anticipated. Initially the World Health Assembly set 2000 as the year of eradication. Now the best guess is sometime in 2007. Wild (as opposed to vaccine-derived) poliovirus is circulating in Nigeria, India, Pakistan and Afghanistan, in descending order of known cases. The virus has spread from Nigeria and India to cause renewed infection in formerly polio-free countries. Making eradication all the more difficult, highly evolved oral vaccine-derived polioviruses have been found in several other countries and, in 2005, even spread within one community of unimmunized people in the United States.
Still, the campaign has made dramatic gains. When it began, an estimated 350,000 to 500,000 children per year worldwide were contracting acute flaccid paralysis, and many died. In 2005 there were only about 1,900 cases. China, with more than a fifth of the world’s population, has been polio-free since 1994. Bangladesh, Egypt and Niger, where the disease had been widespread, have gone more than a year with no cases. Type 2 poliovirus, one of three serotypes—related yet distinct strains that don’t confer cross-immunity—was eradicated in 1999. By most estimates, the quest to rid the planet of polio has saved more than 9 million children.
Yet the poliovirus continues to circulate. And no matter how intently scientists study this foe, many mysteries remain, including why epidemic polio has become such a problem in the first place. Though the virus has probably been with us for centuries or millennia—an Egyptian carving dating as far back as 1580 B.C. shows a priest with a withered leg and a dropped foot, suggestive of paralytic polio—there are no records of epidemic paralytic disease before the nineteenth century. And in 1952, only three years before Jonas E. Salk’s poliovirus vaccine was approved, more than 57,000 children contracted polio in the United States. Why then? And why does polio, an intestinal virus, produce paralytic disease at all?