Where do we go on polio?
‘WE WILL do whatever it takes to eradicate polio,” vows Robert Scott.
The retired physician is chairman of the International PolioPlus committee of Rotary International, which has donated $616 million to the World Health Organization and UNICEF for polio eradication. In 1988, the WHO set 2000 as the deadline for eradication. The next target year was 2005. Now there is none. But the Rotarians have not faltered. “The Rotarian trustees have decided that our No. 1 goal for the year 2006-2007 is that polio eradication is realistic,” Scott declared.
His faith is tonic for scientists working at the Centers for Disease Control and Prevention and the WHO because the idea of eradication is under siege. In May, three prominent scientists -- Isao Arita, Miyuki Nakane and Frank Fenner -- deeply involved in the successful eradication of smallpox worldwide stated in an article in the journal Science that “we believe that global [polio] eradication is unlikely to be achieved.”
Criticism of the polio campaign continues to mount, as the incidence of disease rises. According to the WHO, the number of global cases stood at 1,500 as of October, up from 1,414 during the same period last year. In Nigeria alone, the number of polio victims rose from 522 to 921 for the same period.
The authors of the Science article think that the WHO should abandon its plans to completely stop the transmission of polio. Instead, they favor a strategy of “control” -- regularly scheduled immunizations for children worldwide.
Some longtime polio experts are rethinking the issue as well. Virologist and vaccinologist Stanley Plotkin, for instance, supports eradication, but he also says that “polio is not the biggest problem in tropical areas.... If we fail, we should settle for ‘control’ rather than eradication.”
Linda Venczel, deputy branch chief of polio eradication at the CDC, believes that because the campaign has eradicated polio in the Americas and Europe, it is, to some extent, a victim of its own success. “People don’t see much paralytic polio anymore, so they forget how bad a disease this is,” she said. “In the flush of success from smallpox ... people wanted to eradicate another terrible disease -- they can’t be faulted for that.” Indeed not.
When the polio eradication campaign began in 1988, the disease killed or paralyzed 350,000 children every year. By now, about 5 million children would be crippled or dead without the campaign. But if attempts to eradicate the virus are abandoned, controlling it could be even more elusive.
The recent spike in polio cases has occurred despite the eradication campaign, with its mass-immunization days, its thousands of volunteers, its “Days of Tranquillity” when fighters pause in warring nations so children can be vaccinated. What would happen if routine immunization programs, in which children in developing countries receive vaccinations when they visit clinics, became the main defense against the disease?
Polio would quickly exceed 1988 levels, predicts Roland Sutter, coordinator for research and product development for polio eradication at the WHO. “When I hear ‘control,’ either people are being extremely naive, or very Machiavellian,” he said. “If you know what you’re talking about, you are willing to live with half a million cases of crippled children in a year.... The [polio] program takes longer and costs more money than smallpox eradication.”
The problems that make polio so hard to eradicate make any meaningful attempt at controlling it almost impossible. For one thing, polio is a stealth virus. In a partly immunized population, it can circulate for years undetected, as it did in a Minnesota community in 2005. Furthermore, people with weak immune systems can sometimes shed the virus for decades. Finally, the oral polio vaccine, which consists of live, crippled polio virus, can occasionally produce paralytic disease in children with poor immunity. Even worse, the virulence and transmissibility of the live vaccine virus can increase as it spreads from person to person, causing outbreaks in areas where the naturally occurring polio virus has been eradicated.
The oral vaccine presents other difficulties. In poor, crowded areas such as Uttar Pradesh in northern India, diarrheal infections and malnutrition require that children receive more doses, up to 10 or 12. Yet even after so many doses, some children never develop immunity and still may come down with crippling polio. This doesn’t do much for parents’ confidence in immunization.
After a sudden surge in polio cases, local governments and religious leaders in northern Nigeria suspected that the vaccination was sinister: a Western plot to destroy their daughters’ fertility or kill children. Vaccination rates dropped 30%. Polio spread from Nigeria to 27 countries and as far away as Indonesia.
Because of such setbacks, polio-eradication experts have been forced to acknowledge that the campaign may need some adjustments. The oral vaccine’s problems have led some to call for adding the safe and stable inactivated (or killed) polio virus (an enhanced version of Salk’s original vaccine that is injected) to the arsenal. As Dr. T. Jacob John, a polio expert at the Christian Medical College and Hospital in Vellore, India, points out, each vaccine has properties the other lacks: “One’s defect is covered by the other’s effect.” Although the injected polio virus is more expensive, it provides complete immunity to paralytic disease after two or three doses, even when children are malnourished or suffering from intestinal disease. According to John, a combined schedule of oral and injected vaccines would work well in stopping transmission of wild polio virus, the goal of the eradication campaign.
We are beginning to learn that polio eradication does not necessarily mean a world free of the virus forever. As Eckard Wimmer, a polio virologist at the State University of New York at Stony Brook, showed in a controversial publication in 2002, the virus can easily be synthesized in a laboratory and used as a terrible terror agent in a nonimmunized world. And silently circulating polio virus, whether wild or evolved from the oral vaccine, may also be with us for a long time. We will need worldwide vaccination of children with killed, injected polio vaccine as part of routine immunization for the indefinite future.
