(Corrects paragraph 7 to say smallpox not polio was eradicated)

By Michael Kahn

LONDON, Nov 26 (Reuters) - The global campaign to eradicate polio received a $200 million grant on Monday, a needed cash infusion health officials say will help fund the final push to wipe out the disease.

A world effort to beat polio has succeeded in slashing the number of cases by 99 percent over the past two decades but the virus that causes the disease persists, mainly in Afghanistan, India, Nigeria and Pakistan.

The grant from the Gates Foundation and Rotary International is the catalyst needed to finally eradicate the infection that mostly strikes children under five, said Margaret Chan, Director-General of the World Health Organisation.

"We have the technical tools to do it, and we can achieve a polio-free world if the rest of our financial partners step up to meet the challenge," she said in a statement.

The highly infectious polio virus usually causes common cold symptoms, but in a small percentage of people spreads to the digestive and nervous systems and can cause severe, lasting damage. Survivors can struggle to walk or breathe.

Like smallpox, which in 1979 became the first disease to be eradicated, polio infects only human beings. Polio once killed or paralysed hundreds of thousands of children each year.

Smallpox was eradicated by a global vaccination campaign.

Vaccines developed more than 50 years ago work well against polio but geographic isolation, armed conflict and cultural barriers have kept it from reaching people in the four countries where the disease remains endemic.

In October, the WHO said there has been significant progress in India and Nigeria, which together account for most of the world's 735 reported polio cases so far in 2007. This compares with 1,686 reported cases at the same time last year.

A nearly 20-year effort called the Global Polio Eradication Initiative involving more than 200 countries has succeeded in driving down the number of polio cases worldwide from 350,000 in 1988 to 1,997 in 2006. All but 128 of the cases last year were in India, Nigeria, Afghanistan and Pakistan, the group said.

"The Gates Foundation grant comes at a crucial juncture for the initiative, which urgently needs an infusion of funds to reach the eradication goal," the Gates Foundation and Rotary International said in a statement.

Rotary International received a $100 million grant from the Gates Foundation, which the worldwide organisation of business leaders said it would match over a three-year period.

Most of the initial $100 million will be spent to boost mass immunisation campaigns in the polio-affected countries, polio virus surveillance activities and community education and outreach. (Reporting by Michael Kahn; Editing by Maggie Fox)

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