In 1988, when the World Health Assembly created the Global Polio Eradication Initiative, there were 350,000 cases of wild polio across 125 countries, with more than 1,000 children per day becoming paralyzed. The battle against the disease in recent decades has reduced the cases of wild poliovirus by 99 percent and prevented more than 20 million cases of paralysis. Three poliovirus strains have existed: wild types 1, 2 and 3. The wild types 2 and 3 have been eradicated; type 1 remains endemic in Afghanistan and Pakistan. This isn’t victory, but it is close.
What makes the polio campaign so tantalizing and yet exasperating is that it has often appeared to be on the cusp of eradication, only to see the goal slip away. A new status report from the eradication initiative’s Independent Monitoring Board says the fight against polio is once again at a critical point.
A concerning problem now is the spread of variant poliovirus, or vaccine-derived poliovirus. One of the polio vaccines (not used in the United States since 2000) uses a live, weakened version of the wild strains to trigger an immune response by the human body. Sometimes, if not enough people in a community have been immunized, that strain can genetically revert in the environment to a form that causes paralysis. Cases of the variant polioviruses are especially common in Africa. The type 1 vaccine-derived strain, according to the report, “has an incredible capacity to transmit. It is said to have 10 times greater capacity to paralyse than type 2 vaccine-derived poliovirus.”
Worryingly, the report found “vaccine-derived polioviruses are paralysing nearly 50 times more children than wild polioviruses.” Of the 674 confirmed cases of paralytic poliomyelitis reported during the 12 months up to July 31, just 16 were caused by type 1 wild poliovirus, 217 by circulating type 1 vaccine-derived poliovirus, 436 by circulating type 2 vaccine-derived poliovirus and five by both types of vaccine-derived poliovirus. These cases were reported from 28 countries, 21 of them in Africa.
If the type 1 vaccine-derived poliovirus infects a vulnerable population — where immunization is low — it could easily set off a “chain reaction” and take hold, “a very serious problem that risks destabilizing the whole Polio Programme,” the report warns. It urges polio fighters to press harder against these variant polioviruses.
On top of that worry, lingering barriers to progress remain in Pakistan and Afghanistan. Late last year, there was a surge of wild poliovirus cases in south Khyber Pakhtunkhwa province, in Pakistan’s northwest. The virus has a “stubborn hold” in the region, the report says. One reason: boycotts, in which local populations seek redress for their complaints — job-related, or grievances about lack of basic necessities — and boycott the polio vaccination campaigns. Without immunization coverage, the population remains vulnerable. In Afghanistan, now under the Taliban’s strict Islamist rule, efforts to fight polio with vaccination campaigns face immense obstacles, not the least of which is a severe humanitarian crisis.
The good news is that a new oral polio vaccine that has significantly less risk of seeding new cases is being rolled out; as of this month, 700 million does have been administered across 33 countries.
The report says the goal to interrsupt a new oral polio vaccine that has significantly less risk of seeding new cases is being rolled out; as of this month, 700 million doses have been administered across 33 countries.l certainly be missed. But at this point, with so much invested and so much achieved, the world need not treat failure as inevitable, particularly with a safe new vaccine available. Sustained financial and political support for the battle against polio is essential. So are realistic expectations. As the report notes of the stubborn poliovirus, “once transmission gets established, it takes a long time to get rid of it.”
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