India's Last Bastion of Polio at "Tipping Point": The World Is on the Brink of Eradicating Polio, but Success Depends Largely on Removing the Pocket of Wild Poliovirus in the Indian State of Uttar Pradesh

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The most dangerous form of polio has reached a historic low in a stronghold in India. The single most important pocket of polio--Moradabad and surrounding districts in western Uttar Pradesh--has repeatedly exported wild poliovirus to other states in India and abroad. But epidemiologists there say they have reached a "tipping point" in the eradication campaign.

Polio remains endemic in just four countries--Afghanistan, India, Nigeria and Pakistan--down from 125 countries in 1988. Nine other countries reported importation of poliovirus in 2006. Polio is caused by poliovirus type-1, type-2 or type-3. Type-2 poliovirus was eliminated worldwide in 1999. In 2006 there were 338 cases of type-1 polio in the western part of Uttar Pradesh state. By the end of September 2007, the core

endemic area of the western part of Uttar Pradesh state had been free of type-1 poliovirus for nine months. Never before has the most virulent and most dangerous form of the disease disappeared from its Indian heartland for such a long period. Only four type-1 polio cases had been identified in the whole of western Uttar Pradesh by the end of September 2007. In 2006, the key area had 338 cases.

"The real challenge to global polio eradication is the persistence of type-1 transmission in western Uttar Pradesh," said Dr Harold Jafari, project manager of the World Health Organization's (WHO) National Polio Surveillance Project. "If type-1 can be eliminated here, we can definitively say the war on polio worldwide can be won".

Polio is so resistant to eradication in this part of India because of the combination of extreme poverty, poor sanitation and the high population density. Such conditions facilitate transmission of the virus and compromise the efficacy of the oral vaccine.

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In 2005, India moved away from its exclusive reliance on traditional trivalent oral polio vaccine and started using monovalent oral vaccines, which target either of the remaining two serotypes--type-1 and type-3. These newer vaccines are more efficacious per dose and boost immunity faster than trivalent vaccines.

The following year, however, another outbreak of type-1 polio occurred in India, again in western Uttar Pradesh, following a decline in vaccination coverage. From there, it spread quickly throughout the state and beyond. By the end of the year, 648 confirmed cases of type-1 polio had been declared throughout India.

The government of India embarked on an intensified vaccination strategy in western Uttar Pradesh and the neighbouring Bihar state at the start of 2007. By mid-September Bihar had already conducted 10 vaccination campaigns--a higher level of polio vaccination activity than anywhere else in the world.

This September, the eighth vaccination round was conducted in Moradabad. On the first day of the campaign 604 294 children were immunized at 3445 booths across the Moradabad district. By the end of the round a week later, 946 082 children had been immunized through the district.

"This is definitely our make or break year," said Dr Vibhor Jain, sub-regional team leader for the National Polio Surveillance Project in Moradabad. "There's no room for complacency but, so far, the results are very encouraging."

The logistical challenge of the anti-polio campaign was evident: 1729 vaccination teams visited the more than 700 000 homes of Moradabad district during the September round, covering rural and urban areas. …