An Indian child is vaccinated against polio
The World Health Organization (WHO) has announced a major change of strategy in its campaign to eradicate polio.
From now on, it is going to concentrate on just 13 countries - seven where the disease still occurs, and another six it considers at high risk.
The WHO has spent $2bn on a 15-year campaign to rid the world of polio.
In 1988, when the eradication campaign started, there were around 350,000 cases of polio a year - now there are fewer than 2,000.
Europe, Australasia and the Americas are now polio-free.
But the campaign received a setback last month when it was revealed that the number of cases of the disease rose fourfold last year.
A large outbreak in India accounted for most of the increase.
The WHO strategy has been built on routine vaccinations in countries whose health systems can afford it and mass immunisation campaigns in the developing world.
But spokesman Brent Burkholder said it was now time for a shift of emphasis.
"The shift is just basically that we're focusing now on the endemic countries and the high-risk countries that are remaining.
"We're down to only seven countries now that are really endemic for polio."
Operations will be intensified first in the three nations which together account for 99% of cases - India, Nigeria and Pakistan.
Mass vaccinations will also continue in the other endemic countries - Egypt, Afghanistan, Niger and Somalia.
They will also continue in those considered at risk - Angola, Bangladesh, the Democratic Republic of the Congo, Ethiopia, Nepal and Sudan.
In some of these countries operations have been hindered by war, in others the problem has been public distrust.
The extra operations will cost around a $250m, but in the end, the WHO believes, the world will reap a much larger social and economic benefit if polio can be wiped out in the same way that smallpox was 25 years ago.
The WHO hopes to completely wipe out polio by 2005.
The disease, which once affected millions of children, attacks the central nervous system, often causing paralysis, muscular atrophy and deformity.
Between 5% and 10% of those infected die when their breathing muscles become paralyzed.
It is usually contracted through exposure to contaminated water.