* Pakistan, Afghanistan insecurity hampers vaccinations

* Low Nigeria immunisation rates propels disease in Africa

* New vaccine expected by third quarter of 2009 for India

* "Fragile progress" seen in 21-year eradication campaign

By Laura MacInnis

GENEVA, May 21 (Reuters) - The paralysing polio virus is spreading fast in Pakistan and Afghanistan, two of its last four strongholds, in areas struck by violence and mass displacement, health experts said on Thursday.

A report presented to the World Health Organisation's annual assembly also stressed "the fragility of progress" in the polio fight in India, where vaccinations are being stepped up to better-protect children in fast-growing slums.

Low immunisation rates in Nigeria have caused the virus to spread to eight of its neighbours -- Benin, Burkina Faso, Chad, Cote d'Ivoire, Ghana, Mali, Niger and Togo -- that previously wiped it out, the Global Polio Eradication Campaign said.

Its head Bruce Aylward said that 2008 "was indeed a very difficult year for the eradication programme."

The setbacks seen in both endemic and newly-infected countries reflect "a simple failure to reach and vaccinate children," he told health officials at the Geneva meeting.

Aylward said new vaccines that target all strains of the polio virus in circulation, a particular concern in India, should be ready by the third quarter of this year.

Efforts are underway to distribute oral polio vaccines in 16 countries that have "re-imported" polio since the start of 2008, according to the report that put the last four endemic countries under the spotlight at the World Health Assembly.

A dozen of those countries have reported new cases of paralysis since mid-2008, "demonstrating that international spread of poliovirus is continuing," the report said.

Warfare appears to be the biggest barrier to eradication in Pakistan and Afghanistan, where the number of children paralysed surged in the second half of last year, the report found.

"A deterioration in security resulted in large-scale population movements and outbreaks in polimyelitis-free areas, particularly in the Punjab province of Pakistan," it said.

"By early 2009 poliomyelitis was largely restricted to areas where insecurity hampers supplementary immunisation activities."

When the Global Polio Eradication Initiative was launched in 1988, the contagious disease paralysed more than 1,000 children every day and was endemic in 125 countries around the world.

It has now been stamped out -- at least temporarily -- in all countries except four, thanks to aggressive vaccination campaigns that have cost more than $6 billion to date.

But until outbreaks stop everywhere, epidemiologists say it will continue to spread and threaten more paralysis, further setting off the global eradication goal first slated for 2000.

Iran's delegate to the World Health Assembly expressed "continuing deep concern that the opportunity to eradicate this devastating disease could be squandered." Thailand called the potential continued international spread of polio "an emergency situation that requires action by all parties."

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